Communicable, or infectious diseases, are caused by microorganisms such as bacteria, viruses, parasites and fungi that can be spread, directly or indirectly, from one person to another. Some are transmitted through bites from insects while others are caused by ingesting contaminated food or water.

A variety of disease-producing bacteria and viruses are carried in the mouth, nose, throat and respiratory tract. Conditions such as leprosy, tuberculosis (TB) and different strains of influenza (flu) can be spread by coughing, sneezing, and saliva or mucus on unwashed hands.

Sexually transmitted infections (STIs) such as HIV and viral hepatitis are spread through the exposure to infectious bodily fluids such as blood, vaginal secretions and semen. 

Insects play a significant role in the transmission of disease. For example, bites from Anopheles mosquitoes transmit malaria parasites that can wreak havoc on high-risk populations such as children under age 5 and pregnant women. Yellow fever has also seen resurgence due to reduced vaccination efforts. Many neglected tropical diseases are caused by unsafe water, poor housing conditions and poor sanitation (World Health Organization, n.d.-f).

Globally, the incidence of infectious diseases has declined since 2000, but infectious diseases continue to have major health and economic costs. Infectious diseases can lock people into poverty, undermine the resilience of communities, and have devastating consequences for a country’s economy.

Reducing the spread of infectious diseases globally is beneficial for a population’s health and a country’s economy, and is an essential prerequisite for achieving universal health coverage (UHC). UHC is where everyone can obtain quality health services without suffering financial hardship. However, reaching the goal of UHC requires prevention of and access to quality treatment for infectious diseases, including malaria, TB and HIV, as well as adequate sanitation. It also requires countries to invest resources in pandemic preparedness and the strengthening of their health systems (The World Bank, n.d.).

According to data from the most recent Global Burden of Disease study report, roughly 18.0% of global deaths and 26.4% of global DALYs were attributed to communicable diseases in 2019 (Institute for Health Metrics and Evaluation, n.d.). The burden of disease from communicable diseases disproportionately falls on low-income countries and communities. In fact, when considering only low-income countries rather than global totals, 51.3% of deaths and 58.0% of DALYs were attributed to communicable diseases in 2019, compared to only 5.3% of deaths and 4.6% of DALYs in high-income countries (Institute for Health Metrics and Evaluation, n.d.). The relative importance of communicable diseases is highest among young children: of the ten leading causes of death among children under the age of five globally, seven are communicable diseases (lower respiratory infections like pneumonia, diarrheal diseases, malaria, meningitis, whooping cough, sexually transmitted infections, and measles) (Skolnik, 2023). Overall, more than 80% of deaths and DALYs among children under five globally can be attributed to communicable disease (Institute for Health Metrics and Evaluation, n.d.). A number of social, economic, and environmental determinants of health contribute to the burden of infectious diseases in these contexts including: “availability of safe drinking water and basic sanitation, housing conditions, climate change risks, gender inequity, sociocultural factors, and poverty, among others (Pan American Health Organization, n.d.).” 

“In addition to economic costs, communicable diseases impose intangible social costs on individuals, families, and communities. In sum, the burden of these diseases, with their health, economic, and social costs, prevents the full achievement of health and highlights the need to step up disease elimination efforts” (Pan American Health Organization, n.d.).

According to Skolnik (2023), a number of public health strategies can be used to successfully control communicable diseases, including the following: 

• Vaccinations

• Mass chemotherapy 

• Vector control

• Improved water, sanitation, and hygiene

• Improved care seeking and disease recognition (especially for young children) 

• Improved caregiving and case management or treatment

• Improved surveillance, reporting, and containment

• Behavioral change 

Information about some of the most significant communicable diseases follows, along with information about vector borne diseases, neglected tropical diseases (NTDs), and vaccines and immunizations that are important on the global health agenda.  

HIV 

(World Health Organization, 2022j)

Key facts

• To reach the new proposed global 95–95–95 targets set by UNAIDS, we will need to redouble our efforts to avoid the worst-case scenario of 7.7 million HIV-related deaths over the next 10 years, increasing HIV infections due to HIV service disruptions during COVID-19, and the slowing public health response to HIV.

• HIV continues to be a major global public health issue, having claimed 40.1 million [33.6–48.6 million] lives so far.

• In 2021, 650,000 [510,000–860,000] people died from HIV-related causes and 1.5 million [1.1–2.0 million] people acquired HIV.

• No cure exists for HIV infection. However, with increasing access to effective HIV prevention, diagnosis, treatment and care, including for opportunistic infections, HIV infection has become a manageable chronic health condition, enabling people living with HIV to lead long and healthy lives.

• There were an estimated 38.4 million [33.9–43.8 million] people living with HIV at the end of 2021, two thirds of whom (25.6 million) are in the WHO African Region.

Overview

The human immunodeficiency virus (HIV) targets the immune system and weakens people's defense against many infections and some types of cancer that people with healthy immune systems can more easily fight off. As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. Immune function is typically measured by CD4 cell count.

The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which can take many years to develop if not treated, depending on the individual. AIDS is defined by the development of certain cancers, infections or other severe long-term clinical manifestations.

Signs and Symptoms

The symptoms of HIV vary depending on the stage of infection. Though people living with HIV tend to be most infectious in the first few months after being infected, many are unaware of their status until the later stages. In the first few weeks after initial infection people may experience no symptoms or an influenza-like illness including fever, headache, rash or sore throat.

As the infection progressively weakens the immune system, individuals affected by HIV can develop other signs and symptoms, such as swollen lymph nodes, weight loss, fever, diarrhea and cough. Without treatment, these individuals could also develop severe illnesses such as tuberculosis (TB), cryptococcal meningitis, severe bacterial infections, and cancers such as lymphomas and Kaposi's sarcoma.

Transmission

HIV can be transmitted via the exchange of a variety of body fluids from infected people, such as blood, breast milk, semen and vaginal secretions. HIV can also be transmitted from a mother to her child during pregnancy and delivery. Individuals cannot become infected through ordinary day-to-day contact such as kissing, hugging, shaking hands, or sharing personal objects, food or water. 

It is important to note that people with HIV who are taking ART and are virally suppressed do not transmit HIV to their sexual partners. Early access to ART and support to remain on treatment is therefore critical not only to improve the health of people with HIV but also to prevent HIV transmission.

Risk Factors

Behaviors and conditions that put individuals at greater risk of contracting HIV include:

• having condomless anal or vaginal sex;

• having another sexually transmitted infection (STI) such as syphilis, herpes, chlamydia, gonorrhea and bacterial vaginosis; 

• engaging in harmful use of alcohol and drugs in the context of sexual behavior;

• sharing contaminated needles, syringes and other injecting equipment and drug solutions when injecting drugs;

• receiving unsafe injections, blood transfusions and tissue transplantation, and medical procedures that involve unsterile cutting or piercing; and

• experiencing accidental needle stick injuries, including among health workers.

Diagnosis

HIV can be diagnosed through rapid diagnostic tests that provide same-day results. This greatly facilitates early diagnosis and linkage with treatment and care. People can also use HIV self-tests to test themselves. However, no single test can provide a full HIV positive diagnosis; confirmatory testing is required, conducted by a qualified and trained health or community worker at a community center or clinic. HIV infection can be detected with great accuracy using WHO prequalified tests within a nationally approved testing strategy and algorithm.

Most widely-used HIV diagnostic tests detect antibodies produced by the person as part of their immune response to fight HIV. In most cases, people develop antibodies to HIV within 28 days of infection. During this time, people experience the so-called window period – when HIV antibodies haven’t been produced in high enough levels to be detected by standard tests and when they may have had no signs of HIV infection, but also when they may transmit HIV to others. After infection, without treatment and viral suppression, an individual may transmit HIV to a sexual or drug-sharing partner, or a pregnant woman may transmit HIV to her infant during pregnancy or the breastfeeding period.

Following a positive diagnosis, people should be retested before they are enrolled in treatment and care to rule out any potential testing or reporting error prior to starting life-long treatment. It is important to support people with HIV to stay on treatment and provide counseling messages and services when they are concerned about the accuracy of their diagnosis or if they stop treatment and care and need to be re-engaged. 

While testing for adolescents and adults has been made simple and efficient, this is not the case for babies born to HIV-positive mothers. For children less than 18 months of age, rapid antibody testing is not sufficient to identify HIV infection – virological testing must be provided as early as birth or at 6 weeks of age. New technologies are now available to perform this test at the point of care and enable same-day results, which will accelerate appropriate linkage with treatment and care.

Prevention

Individuals can reduce the risk of HIV infection by limiting exposure to risk factors. Key approaches for HIV prevention, which are often used in combination, include:

• male and female condom use;

• prevention, testing and counseling for HIV and STIs;

• voluntary medical male circumcision (VMMC);

• use of antiretroviral drugs (ARVs) for prevention (oral PrEP and long acting products), the dapivirine vaginal ring and injectable long-acting cabotegravir;

• harm reduction for people who inject and use drugs; and

• elimination of mother-to-child transmission (MTCT) of HIV.

HIV is not transmitted if a person’s sexual partner is virally suppressed on ART, so increasing access to testing and supporting linkage to ART is an important component of HIV prevention. 

Treatment

HIV disease can be managed by treatment regimens composed of a combination of antiretroviral (ARV) drugs. Current antiretroviral therapy (ART) does not cure HIV infection, but it suppresses viral replication and allows an individual's immune system recovery to strengthen and regain the capacity to fight off opportunistic infections and some cancers.

Since 2016, WHO has recommended Treat All. This policy states that all people living with HIV should be provided with lifelong ART, including children, adolescents, adults and pregnant and breastfeeding women, regardless of their clinical status or CD4 cell count. 

By June 2022, 189 countries had already adopted this recommendation, covering 99% of all people living with HIV globally. In addition to the Treat All strategy, WHO recommends a rapid ART initiation to all people living with HIV, including offering ART on the same day as diagnosis among those who are ready to start treatment. By June 2022, 97 countries reported that they have adopted this policy, and almost two-thirds of them reported country-wide implementation.

Globally, 28.7 million people living with HIV were receiving ART in 2021. Global ART coverage was 75% [66–85%] in 2021. However, more efforts are needed to scale up treatment, particularly for children and adolescents. Only 52% [42–65%] of children (0–14 years old) were receiving ART at the end of 2021.

Advanced HIV disease remains a persistent problem in the HIV response. People continue to present or re-present for care with advanced immune suppression, putting them at a higher risk of developing opportunistic infections. WHO is supporting countries to implement the advanced HIV disease package of care to reduce illness and death. 

Tuberculosis 

(World Health Organization, 2022i)

Key facts

• A total of 1.6 million people died from TB in 2021 (including 187,000 people with HIV). Worldwide, TB is the 13th leading cause of death and the second leading infectious killer after COVID-19 (above HIV/AIDS).

• In 2021, an estimated 10.6 million people fell ill with tuberculosis (TB) worldwide. Six million men, 3.4 million women and 1.2 million children. TB is present in all countries and age groups, but TB is curable and preventable.

• In 2021, 1.2 million children fell ill with TB globally. Child and adolescent TB is often overlooked by health providers and can be difficult to diagnose and treat.

• In 2021, the 30 high TB burden countries accounted for 87% of new TB cases

• Multidrug-resistant TB (MDR-TB) remains a public health crisis and a health security threat. Only about one in three people with drug resistant TB accessed treatment in 2020.

• Globally, TB incidence is falling at about 2% per year and between 2015 and 2020 the cumulative reduction was 11%. This was over half way to the End TB Strategy milestone of 20% reduction between 2015 and 2020.

• An estimated 66 million lives were saved through TB diagnosis and treatment between 2000 and 2020.

• Globally, close to one in two TB-affected households face costs higher than 20% of their household income, according to latest national TB patient cost survey data. The world did not reach the milestone of 0% TB patients and their households facing catastrophic costs as a result of TB disease by 2020.

• By 2022, US$ 13 billion is needed annually for TB prevention, diagnosis, treatment and care to achieve the global target agreed at the UN high level-meeting on TB in 2018.

• Funding in low- and middle-income countries (LMICs) that account for 98% of reported TB cases falls far short of what is needed. Spending in 2020 amounted to US$ 5.3 billion less than half (41%) of the global target.

• There was an 8.7% decline in spending between 2019 and 2020 (from US$ 5.8 billion to US$ 5.3 billion), with TB funding in 2020 back to the level of 2016.

• Ending the TB epidemic by 2030 is among the health targets of the United Nations Sustainable Development Goals (SDGs).

Tuberculosis (TB) is caused by bacteria (Mycobacterium tuberculosis) that most often affect the lungs. Tuberculosis is curable and preventable.

TB is spread from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB germs into the air. A person needs to inhale only a few of these germs to become infected.

About a quarter of the global population is estimated to have been infected with TB bacteria, but most people will not go on to develop TB disease and some will clear the infection. Those who are infected but not (yet) ill with the disease cannot transmit it.

People infected with TB bacteria have a 5–10% lifetime risk of falling ill with TB. Those with compromised immune systems, such as people living with HIV, malnutrition or diabetes, or people who use tobacco, have a higher risk of falling ill.

When a person develops active TB disease, the symptoms, such as cough, fever, night sweats, or weight loss, may be mild for many months. This can lead to delays in seeking care, and results in transmission of the bacteria to others. People with active TB can infect 5–15 other people through close contact over the course of a year. Without proper treatment, 45% of HIV-negative people with TB on average and nearly all HIV-positive people with TB will die.

Who is most at risk?

Tuberculosis mostly affects adults in their most productive years. However, all age groups are at risk. Over 80% of cases and deaths are in low- and middle-income countries.

People who are infected with HIV are 16 times more likely to develop active TB. The risk of active TB is also greater in persons suffering from other conditions that impair the immune system. People with undernutrition are three times more at risk. Globally in 2021, there were 2.2 million new TB cases that were attributable to undernutrition.

Alcohol use disorder and tobacco smoking increase the risk of TB. In 2021, 0.74 million new TB cases worldwide were attributable to alcohol use disorder and 0.69 million were attributable to smoking.

Global impact of TB

TB occurs in every part of the world. In 2021, the largest number of new TB cases occurred in the WHO South-East Asian Region, with 46% of new cases, followed by the WHO African Region, with 23% of new cases and the WHO Western Pacific with 18%. 

In 2020, 87% of new TB cases occurred in the 30 high TB burden countries. Eight countries accounted for more than two thirds of the global total: India, Indonesia, China, the Philippines, Pakistan, Nigeria, Bangladesh and the Democratic Republic of the Congo. 

Symptoms and diagnosis

Common symptoms of active lung TB are cough with sputum and blood at times, chest pains, weakness, weight loss, fever and night sweats. WHO recommends the use of rapid molecular diagnostic tests as the initial diagnostic test in all persons with signs and symptoms of TB as they have high diagnostic accuracy and will lead to major improvements in the early detection of TB and drug-resistant TB. Rapid tests recommended by WHO are the Xpert MTB/RIF Ultra and Truenat assays. 

Diagnosing multidrug-resistant and other resistant forms of TB as well as HIV-associated TB can be complex and expensive. 

Tuberculosis is particularly difficult to diagnose in children.

Treatment

TB is a treatable and curable disease. Drug-susceptible TB disease is treated with a standard 4-month or 6-month course of four antimicrobial drugs that are provided with support to the patient by a health worker or trained treatment supporter. Without such support, treatment adherence is more difficult.

Since 2000, an estimated 74 million lives have been saved through TB diagnosis and treatment.

TB and HIV

People living with HIV are 16 (Uncertainty interval: 14–18) times more likely to fall ill with TB disease than people without HIV.

HIV and TB form a lethal combination, each speeding the other's progress. In 2021, about 187 000 people died of HIV-associated TB. The percentage of notified TB patients who had a documented HIV test result in 2021 was only 76%, up from 73% in 2020. The WHO African Region, has the highest burden of HIV-associated TB Overall in 2021, only 46% of TB patients known to be living with HIV were on ART.

WHO recommends a 12-component approach of collaborative TB-HIV activities, including actions for prevention and treatment of infection and disease, to reduce deaths.

Multidrug-resistant TB

TB medicines have been used for decades and strains that are resistant to one or more of the medicines have been documented in every country surveyed. Drug resistance emerges when TB medicines are used inappropriately, through incorrect prescription by health care providers, poor quality drugs, and patients stopping treatment prematurely.

Multidrug-resistant tuberculosis (MDR-TB) is a form of TB caused by bacteria that do not respond to isoniazid and rifampicin, the two most effective first-line TB drugs. MDR-TB is treatable and curable by using second-line drugs. However, second-line treatment options are limited and require extensive chemotherapy (of at least nine months and up to 20 months of treatment) with medicines that are expensive and toxic.

In some cases, more extensive drug resistance can develop. TB caused by bacteria that do not respond to the most effective second-line TB drugs can leave patients with limited treatment options.

MDR-TB remains a public health crisis and a health security threat. 

In accordance with WHO guidelines, detection of MDR/RR-TB requires bacteriological confirmation of TB and testing for drug resistance using rapid molecular tests, culture methods or sequencing technologies. 

Treatment of MDR/RR-TB requires a course of second-line drugs for at least nine months and up to 20 months, supported by counseling and monitoring for adverse events. WHO recommends expanded access to all-oral regimens.

Only about one in three people with drug resistant TB accessed treatment in 2020.

Worldwide in 2019, the treatment success rate of MDR/RR-TB patients was 60%. In 2020, WHO recommended a new shorter (9–11 months) and fully oral regimen for patients with MDB-TB. Research findings have shown that patients find it easier to complete the regimen, compared with the longer regimens that last up to 20 months. Resistance to fluoroquinolones should be excluded prior to the initiation of treatment with this regimen.

By the end of 2021, 92 countries started using shorter MDR-TB treatment regimens and 109 had started using bedaquiline, in an effort to improve the effectiveness of MDR-TB treatment.

Catastrophic cost 

WHO’s End TB Strategy target of “No TB patients and their households facing catastrophic costs as a result of TB disease”, monitored by countries and WHO since WHA67.1 End TB Strategy was adopted in 2015, shows that the world did not reach the milestone of 0% by 2020.

According to the results of 27 national surveys on costs faced by TB patients and their households, the percentage facing catastrophic costs* ranged from 13% to 92% and the pooled average, weighted for each country’s number of notified cases, was 48% 

*total costs > 20% annual household income

Investments in TB prevention, diagnosis and treatment and research

US$ 13 billion are needed annually for TB prevention, diagnosis, treatment and care to achieve global targets agreed on at the UN high level-TB meeting. 

• There was a decline in global spending on essential TB services from US$ 6.0 billion in 2019 to US$ 5.4 billion in 2021, which is less than half of the global target.

• Of the US$5.4 billion spent on tuberculosis care and services in 2021, 79% was from domestic sources, with the BRICS countries (Brazil, Russian Federation, India, China and South Africa) accounting for US$2.7 billion (64% of total domestic funding).

In low- and middle-income countries, international donor funding remains crucial. The main source is the Global Fund to Fight AIDS, Tuberculosis and Malaria (the Global Fund). 

• The United States (US) Government is the largest contributor of funding to the Global Fund and also the largest bilateral donor; overall, it contributes close to 50% of international donor funding for TB.

• For research and development, according to the Treatment Action Group, only US$ 0.9 billion were available in 2020 of the US$2 billion required per year to accelerate the development of new tools. At least an extra US$1.1 billion per year is needed to accelerate the development of new tools.  

Malaria 

(World Health Organization, 2022m)

Key facts

• Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It is preventable and curable.

• In 2021, there were an estimated 247 million cases of malaria worldwide.

• The estimated number of malaria deaths stood at 619 000 in 2021.

• The WHO African Region carries a disproportionately high share of the global malaria burden. In 2021, the region was home to 95% of malaria cases and 96% of malaria deaths. Children under 5 accounted for about 80% of all malaria deaths in the Region.

Overview

Malaria is an acute febrile illness caused by Plasmodium parasites, which are spread to people through the bites of infected female Anopheles mosquitoes. Five parasite species cause malaria in humans, and two of these species – P. falciparum and P. vivax – pose the greatest threat. P. falciparum is the deadliest malaria parasite and the most prevalent on the African continent. P. vivax is the dominant malaria parasite in most countries outside of sub-Saharan Africa. 

The first symptoms – fever, headache and chills – usually appear 10–15 days after the infective mosquito bite and may be mild and difficult to recognize as malaria. Left untreated, P. falciparum malaria can progress to severe illness and death within a period of 24 hours.

In 2021, nearly half of the world's population was at risk of malaria. Some population groups are at considerably higher risk of contracting malaria and developing severe disease: infants, children under five years of age, pregnant women and patients with HIV/AIDS, as well as people with low immunity moving to areas with intense malaria transmission such as migrant workers, mobile populations and travelers. 

Disease burden

According to the latest World malaria report (World Health Organization, 2022n), there were 247 million cases of malaria in 2021 compared to 245 million cases in 2020. The estimated number of malaria deaths stood at 619,000 in 2021 compared to 625,000 in 2020. 

Over the two peak years of the COVID-19 pandemic (2020–2021), COVID-related disruptions led to about 13 million more malaria cases and 63,000 more malaria deaths. The WHO African Region continues to carry a disproportionately high share of the global malaria burden. In 2021 the Region was home to about 95% of all malaria cases and 96% of deaths. Children under five years of age accounted for about 80% of all malaria deaths in the Region.

Four African countries accounted for just over half of all malaria deaths worldwide: Nigeria (31.3%), the Democratic Republic of the Congo (12.6%), United Republic of Tanzania (4.1%) and Niger (3.9%).

Prevention

Over the last two decades, expanded access to WHO-recommended malaria prevention tools and strategies – including effective vector control and the use of preventive antimalarial drugs – has had a major impact in reducing the global burden of this disease.

Vector control

(World Health Organization, n.d.-i)

Vector control is a vital component of malaria control and elimination strategies as it is highly effective in preventing infection and reducing disease transmission. The 2 core interventions are insecticide-treated nets (ITNs) and indoor residual spraying (IRS). 

Progress in global malaria control is threatened by emerging resistance to insecticides among Anopheles mosquitoes. As described in the latest World malaria report, other threats to ITNs include insufficient access, loss of nets due to the stresses of day-to-day life outpacing replacement, and changing behavior of mosquitoes, which appear to be biting early before people go to bed and resting outdoors, thereby evading exposure to insecticides.

Preventive chemotherapies

(World Health Organization, n.d.-e)

Preventive chemotherapy is the use of medicines, either alone or in combination, to prevent malaria infections and their consequences. It requires giving a full treatment course of an antimalarial medicine to vulnerable populations (generally infants, children under 5 years of age and pregnant women) at designated time points during the period of greatest malarial risk, regardless of whether the recipients are infected with malaria. Preventive chemotherapy includes perennial malaria chemoprevention (PMC), seasonal malaria chemoprevention (SMC), intermittent preventive treatment of malaria in pregnancy (IPTp) and school-aged children (IPTsc), post-discharge malaria chemoprevention (PDMC) and mass drug administration (MDA). These safe and cost-effective strategies are intended to complement ongoing malaria control activities, including vector control measures, prompt diagnosis of suspected malaria, and treatment of confirmed cases with antimalarial medicines.

Vaccine

Since October 2021, WHO also recommends broad use of the RTS,S/AS01 malaria vaccine among children living in regions with moderate to high P. falciparum malaria transmission. The vaccine has been shown to significantly reduce malaria, and deadly severe malaria, among young children.

Case management 

Early diagnosis and treatment of malaria reduces disease, prevents deaths and contributes to reducing transmission. WHO recommends that all suspected cases of malaria be confirmed using parasite-based diagnostic testing (World Health Organization, n.d.-a) (through either microscopy or a rapid diagnostic test). Diagnostic testing enables health providers to swiftly distinguish between malarial and non-malarial fevers, facilitating appropriate treatment. 

The best available treatment (World Health Organization, n.d.-g), particularly for P. falciparum malaria, is artemisinin-based combination therapy (ACT). The primary objective of treatment is to ensure the rapid and full elimination of Plasmodium parasites to prevent an uncomplicated case of malaria from progressing to severe disease or death. 

Antimalarial drug resistance

Over the last decade, antimalarial drug resistance has emerged as a threat to global malaria control efforts in the Greater Mekong subregion. WHO is also concerned about more recent reports of drug-resistant malaria in Africa. Regular monitoring of drug efficacy is needed to inform treatment policies in malaria-endemic countries, and to ensure early detection of, and response to, drug resistance. 

Elimination

Malaria elimination is defined as the interruption of local transmission of a specified malaria parasite species in a defined geographical area as a result of deliberate activities. Continued measures to prevent re-establishment of transmission are required. 

In 2021, 35 countries reported fewer than 1000 indigenous cases of the disease, up from 33 countries in 2020 and just 13  countries in 2000. Countries that have achieved at least 3 consecutive years of zero indigenous cases of malaria are eligible to apply for the WHO certification of malaria elimination (World Health Organization, n.d.-b). Since 2015, 9 countries have been certified by the WHO Director-General as malaria-free, including Maldives (2015), Sri Lanka (2016), Kyrgyzstan (2016), Paraguay (2018), Uzbekistan (2018), Argentina (2019), Algeria (2019), China (2021) and El Salvador (2021).

(World Health Organization, 2021d)

Surveillance

Malaria surveillance is the continuous and systematic collection, analysis and interpretation of malaria-related data, and the use of that data in the planning, implementation and evaluation of public health practice. Improved surveillance of malaria cases and deaths helps ministries of health determine which areas or population groups are most affected and enables countries to monitor changing disease patterns. Strong malaria surveillance systems also help countries design effective health interventions and evaluate the impact of their malaria control programmes.

Pneumonia in children 

(World Health Organization, 2022k)

Key facts

• Pneumonia accounts for 14% of all deaths of children under 5 years old, killing 740 180 children in 2019.

• Pneumonia can be caused by viruses, bacteria or fungi.

• Pneumonia can be prevented by immunization, adequate nutrition, and by addressing environmental factors.

• Pneumonia caused by bacteria can be treated with antibiotics, but only one third of children with pneumonia receive the antibiotics they need.

Overview

Pneumonia is a form of acute respiratory infection that affects the lungs. The lungs are made up of small sacs called alveoli, which fill with air when a healthy person breathes. When an individual has pneumonia, the alveoli are filled with pus and fluid, which makes breathing painful and limits oxygen intake.

Pneumonia is the single largest infectious cause of death in children worldwide. Pneumonia killed 740 180 children under the age of 5 in 2019, accounting for 14% of all deaths of children under 5 years old but 22% of all deaths in children aged 1 to 5 years. Pneumonia affects children and families everywhere, but deaths are highest in southern Asia and sub-Saharan Africa. Children can be protected from pneumonia, it can be prevented with simple interventions, and it can be treated with low-cost, low-tech medication and care.

Causes

Pneumonia is caused by several infectious agents, including viruses, bacteria and fungi. The most common are the following.

• Streptococcus pneumoniae is the most common cause of bacterial pneumonia in children. 

• Haemophilus influenzae type b (Hib) is the second most common cause of bacterial pneumonia. 

• Respiratory syncytial virus is the most common viral cause of pneumonia.

• In infants infected with HIV, Pneumocystis jiroveci is one of the most common causes of pneumonia, responsible for at least one quarter of all pneumonia deaths in HIV-infected infants.

Transmission

Pneumonia can be spread in several ways. The viruses and bacteria that are commonly found in a child's nose or throat can infect the lungs if they are inhaled. They may also spread via air-borne droplets from a cough or sneeze. In addition, pneumonia may spread through blood, especially during and shortly after birth. More research needs to be done on the different pathogens causing pneumonia and the ways they are transmitted, as this is of critical importance for treatment and prevention.

Presenting features

The presenting features of viral and bacterial pneumonia are similar. However, the symptoms of viral pneumonia may be more numerous than the symptoms of bacterial pneumonia. In children under 5 years of age who have cough and/or difficult breathing, with or without fever, pneumonia is diagnosed by the presence of either fast breathing or lower chest wall indrawing where their chest moves in or retracts during inhalation (in a healthy person, the chest expands during inhalation). Wheezing is more common in viral infections.

Very severely ill infants may be unable to feed or drink and may also experience unconsciousness, hypothermia and convulsions.

Risk factors

While most healthy children can fight the infection with their natural defenses, children whose immune systems are compromised are at higher risk of developing pneumonia. A child's immune system may be weakened by malnutrition or undernourishment, especially in infants who are not exclusively breastfed. 

Pre-existing illnesses, such as symptomatic HIV infections and measles, also increase a child's risk of contracting pneumonia. 

The following environmental factors also increase a child's susceptibility to pneumonia:

• indoor air pollution caused by cooking and heating with biomass fuels (such as wood or dung)

• living in crowded homes

• parental smoking.

Treatment

Pneumonia should be treated with antibiotics. The antibiotic of choice for first line treatment is amoxicillin dispersible tablets. Most cases of pneumonia require oral antibiotics, which are often prescribed at a health center. These cases can also be diagnosed and treated with inexpensive oral antibiotics at the community level by trained community health workers. Hospitalization is recommended only for severe cases of pneumonia.

Prevention

Preventing pneumonia in children is an essential component of a strategy to reduce child mortality. Immunization against Hib, pneumococcus, measles and whooping cough (pertussis) is the most effective way to prevent pneumonia. 

Adequate nutrition is key to improving children's natural defenses, starting with exclusive breastfeeding for the first 6 months of life. In addition to being effective in preventing pneumonia, it also helps to reduce the length of the illness if a child does become ill.

Addressing environmental factors such as indoor air pollution (by providing affordable clean indoor stoves, for example) and encouraging good hygiene in crowded homes also reduces the number of children who fall ill with pneumonia. 

In children infected with HIV, the antibiotic cotrimoxazole is given daily to decrease the risk of contracting pneumonia.

Diarrheal disease 

(World Health Organization, 2017)

Key facts

• Diarrheal disease is the second leading cause of death in children under five years old. It is both preventable and treatable.

• Each year diarrhea kills around 525 000 children under five.

• A significant proportion of diarrheal disease can be prevented through safe drinking-water and adequate sanitation and hygiene.

• Globally, nearly 1.7 billion cases of childhood diarrheal disease occur every year.

• Diarrhea is a leading cause of malnutrition in children under five years old.

Diarrheal disease is the second leading cause of death in children under five years old, and is responsible for killing around 525 000 children every year. Diarrhea can last several days, and can leave the body without the water and salts that are necessary for survival. In the past, for most people, severe dehydration and fluid loss were the main causes of diarrhea deaths. Now, other causes such as septic bacterial infections are likely to account for an increasing proportion of all diarrhea-associated deaths. Children who are malnourished or have impaired immunity as well as people living with HIV are most at risk of life-threatening diarrhea.

Diarrhea is defined as the passage of three or more loose or liquid stools per day (or more frequent passage than is normal for the individual). Frequent passing of formed stools is not diarrhea, nor is the passing of loose, "pasty" stools by breastfed babies. 

Diarrhea is usually a symptom of an infection in the intestinal tract, which can be caused by a variety of bacterial, viral and parasitic organisms. Infection is spread through contaminated food or drinking-water, or from person-to-person as a result of poor hygiene. 

Interventions to prevent diarrhea, including safe drinking-water, use of improved sanitation and hand washing with soap can reduce disease risk. Diarrhea should be treated with oral rehydration solution (ORS), a solution of clean water, sugar and salt. In addition, a 10-14 day supplemental treatment course of dispersible 20 mg zinc tablets shortens diarrhea duration and improves outcomes.

Diarrhea has three clinical types:

• acute watery diarrhea – lasts several hours or days, and includes cholera;

• acute bloody diarrhea – also called dysentery; and 

• persistent diarrhea – lasts 14 days or longer. 

Scope of diarrheal disease

Diarrheal disease is a leading cause of child mortality and morbidity in the world, and mostly results from contaminated food and water sources. Worldwide, 780 million individuals lack access to improved drinking-water and 2.5 billion lack improved sanitation. Diarrhea due to infection is widespread throughout developing countries.

In low-income countries, children under three years old experience on average three episodes of diarrhea every year. Each episode deprives the child of the nutrition necessary for growth. As a result, diarrhea is a major cause of malnutrition, and malnourished children are more likely to fall ill from diarrhea.

Dehydration

The most severe threat posed by diarrhea is dehydration. During a diarrheal episode, water and electrolytes (sodium, chloride, potassium and bicarbonate) are lost through liquid stools, vomit, sweat, urine and breathing. Dehydration occurs when these losses are not replaced.

The degree of dehydration is rated on a scale of three.

1. Severe dehydration (at least two of the following signs):

• lethargy/unconsciousness

• sunken eyes

• unable to drink or drink poorly

• skin pinch goes back very slowly ( ≥2 seconds)

2. Some dehydration (two or more of the following signs):

• restlessness, irritability

• sunken eyes

• drinks eagerly, thirsty

3. No dehydration (not enough signs to classify as some or severe dehydration).

Causes

Infection: diarrhea is a symptom of infections caused by a host of bacterial, viral and parasitic organisms, most of which are spread by feces-contaminated water. Infection is more common during a shortage of adequate sanitation and hygiene and safe water for drinking, cooking and cleaning. Rotavirus and Escherichia coli, are the two most common etiological agents of moderate-to-severe diarrhea in low-income countries. Other pathogens such as cryptosporidium and shigella species may also be important. Location-specific etiologic patterns also need to be considered.

Malnutrition: Children who die from diarrhea often suffer from underlying malnutrition, which makes them more vulnerable to diarrhea. Each diarrheal episode, in turn, makes their malnutrition even worse. diarrhea is a leading cause of malnutrition in children under five years old.

Source: Water contaminated with human feces, for example, from sewage, septic tanks and latrines, is of particular concern. Animal feces also contain microorganisms that can cause diarrhea.

Other causes: diarrheal disease can also spread from person-to-person, aggravated by poor personal hygiene. Food is another major cause of diarrhea when it is prepared or stored in unhygienic conditions. Unsafe domestic water storage and handling is also an important risk factor. Fish and seafood from polluted water may also contribute to the disease.

Prevention and treatment

Key measures to prevent diarrhea include:

• access to safe drinking-water;

• use of improved sanitation;

• hand washing with soap;

• exclusive breastfeeding for the first six months of life;

• good personal and food hygiene;

• health education about how infections spread; and

• rotavirus vaccination. 

Key measures to treat diarrhea include the following:

• Rehydration: with oral rehydration salts (ORS) solution. ORS is a mixture of clean water, salt and sugar. It costs a few cents per treatment. ORS is absorbed in the small intestine and replaces the water and electrolytes lost in the feces. 

• Zinc supplements: zinc supplements reduce the duration of a diarrhea episode by 25% and are associated with a 30% reduction in stool volume. 

• Rehydration: with intravenous fluids in case of severe dehydration or shock.

• Nutrient-rich foods: the vicious circle of malnutrition and diarrhea can be broken by continuing to give nutrient-rich foods – including breast milk – during an episode, and by giving a nutritious diet – including exclusive breastfeeding for the first six months of life – to children when they are well. 

• Consulting a health professional, in particular for management of persistent diarrhea or when there is blood in stool or signs of dehydration. 

Vector-borne diseases  

(World Health Organization, 2020a)

Key facts

• Vector-borne diseases account for more than 17% of all infectious diseases, causing more than 700,000 deaths annually. They can be caused by either parasites, bacteria or viruses.
• Malaria is a parasitic infection transmitted by Anopheline mosquitoes. It causes an estimated 219 million cases globally, and results in more than 400,000 deaths every year. Most of the deaths occur in children under the age of 5 years.
• Dengue is the most prevalent viral infection transmitted by Aedes mosquitoes. More than 3.9 billion people in over 129 countries are at risk of contracting dengue, with an estimated 96 million symptomatic cases and an estimated 40,000 deaths every year.
• Other viral diseases transmitted by vectors include chikungunya fever, Zika virus fever, yellow fever, West Nile fever, Japanese encephalitis (all transmitted by mosquitoes), tick-borne encephalitis (transmitted by ticks).
• Many vector-borne diseases are preventable through protective measures and community mobilization.

Vectors

Vectors are living organisms that can transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are bloodsucking insects, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later transmit it into a new host, after the pathogen has replicated. Often, once a vector becomes infectious, they are capable of transmitting the pathogen for the rest of their life during each subsequent bite/blood meal. 

Vector-borne diseases 

Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors. Every year more than 700,000 people die from diseases such as malaria, dengue, schistosomiasis, human African trypanosomiasis, leishmaniasis, Chagas disease, yellow fever, Japanese encephalitis, and onchocerciasis. 

The burden of these diseases is highest in tropical and subtropical areas, and they disproportionately affect the poorest populations. Since 2014, major outbreaks of dengue, malaria, chikungunya, yellow fever and Zika have afflicted populations, claimed lives, and overwhelmed health systems in many countries. Other diseases such as Chikungunya, leishmaniasis, and lymphatic filariasis cause chronic suffering, life-long morbidity, disability, and occasional stigmatization. 

Distribution of vector-borne diseases is determined by a complex set of demographic, environmental, and social factors, including global travel and trade, and unplanned urbanization.

The following table is a non-exhaustive list of vector-borne diseases, ordered according to the vector by which each disease is transmitted. The list also illustrates the type of pathogen that causes the disease in humans. 

A crucial element in reducing the burden of vector-borne diseases is behavioral change. WHO works with partners to provide education and improve public awareness so that people know how to protect themselves and their communities from mosquitoes, ticks, bugs, flies, and other vectors.

Access to water and sanitation is a very important factor in disease control and elimination. WHO works together with many different government sectors to improve water storage and sanitation, thereby helping to control these diseases at the community level.

Neglected Tropical Diseases 

(World Health Organization, n.d.-d)

Neglected tropical diseases (NTDs) are a diverse group of 20 conditions that are mainly prevalent in tropical areas, where they mostly affect impoverished communities and disproportionately affect women and children. These diseases cause devastating health, social and economic consequences to more than one billion people worldwide.

The epidemiology of NTDs is complex and often related to environmental conditions. Many of them are vector-borne, have animal reservoirs, and are associated with complex life cycles. All of these factors make the control of NTDs challenging. 

How can Diseases be Eradicated or Eliminated?

• Elimination = reduction of incidence to zero, but continued intervention is required to prevent new incidents. For example, neonatal tetanus was eliminated.

• Eradication = reduction of incidence to zero and no continued intervention is required. Examples of eradication are smallpox and rinderpest (Dowdle, 1999).

• Eradicable Disease = a disease that realistically could be eradicated with current technology. A disease may be considered eradicable if these criteria are met:
• Disease is infectious
• Humans are the major host
• Effective vaccines and treatments are available
• Political and financial support exist for eradication

The International Task Force for Disease Eradication (ITFDE) has determined that seven diseases are currently eradicable: polio, Guinea worm disease, lymphatic filariasis, cysticercosis, measles, mumps and rubella (Roser et al., 2014).

• Elimination as a public health problem globally = prevalence of less than 1 per 10,000 population. For example, leprosy was declared eliminated as a global public health problem in 2000, although 120 countries still reported cases. Most countries reported it eliminated as a public health problem by 2010. In 2019, 45 countries reported zero cases of leprosy (World Health Organization, 2023f).

NTDs include the following:

• Buruli ulcer: a chronic skin disease caused by Mycobacterium ulcerans from the environment. It usually starts with a painless swelling but can eventually cause deformities of the bones. The mode of transmission and means of prevention are unknown (World Health Organization, 2023a). 
• Chagas disease: a parasitic disease found mostly in developing countries in the Americas. It is transmitted by bites from insects infected with a protozoan, and the parasite enters the body when the bites are scratched. Vector control and hygiene are the best prevention, and effective treatment is available if benznidazole or nifurtimox is given in the acute phase (Pan American Health Organization & World Health Organization, n.d.).
• Dengue: a viral infection transmitted by mosquito bites that has grown dramatically in recent decades. It is treated with rest and hydration. A vaccine has been developed but can be used only for those who have had a past dengue infection. The best prevention is vector control (preventing mosquitoes from breeding and protecting humans from mosquitoes) (World Health Organization, 2022a).
• Chikungunya: a mosquito-borne viral disease with symptoms and transmission similar to those of Dengue, which makes it hard to diagnose. No vaccine or specific treatment exists, and vector control is the best prevention for this disease (World Health Organization, 2022l).
• Dracunculiasis (“Guinea worm disease”): a crippling parasitic disease transmitted by drinking contaminated water. No vaccine or specific medical treatment exists, but efforts by WHO and the Carter Center have improved sanitation and have nearly eradicated this disease. In the 1980s, 20 countries had endemic dracunculiasis with millions of cases reported, but in 2019 as few as 54 cases were reported, from 6 countries. Dracunculiasis is considered eradicable by the ITFDE (World Health Organization, 2022b).
• Echinococcosis: a parasitic disease caused by ingesting tapeworm eggs in contaminated food, water or soil, or after direct contact with animals. This contact is especially dangerous with dogs. Treatment is expensive and complicated and sometimes requires surgery. Prevention is easier with domestic animals that can be periodically dewormed, but wild animals are sometimes involved in transmission (World Health Organization, 2021a).
• Foodborne trematodiases: refers to four different parasitic diseases caught by ingesting parasite larvae in raw fish or vegetables. Transmission is complex, first via a freshwater snail which may be eaten by fish or other animals, and later in the cycle consumed by humans. Various drugs are used for treating the four trematode infections. Prevention with sanitation and food hygiene is recommended, but some cultural eating habits increase the risk of reinfection (World Health Organization, 2021b).
• Human African Trypanosomiasis (“sleeping sickness”):  a parasitic disease found in sub-Saharan Africa, caused by bites from tse-tse flies. Drugs are available to treat it in the early stages, but without treatment it can be fatal. Unfortunately, the first stage of the disease is a long asymptomatic period, which makes diagnosis difficult. Extensive screenings of at-risk populations are recommended (World Health Organization, 2022c).
• Leishmaniasis: a parasitic disease in three forms, transmitted by infected sandflies. The Visceral form is the most serious and is often fatal, the Cutaneous form affects skin, and the Mucocutaneous affects the mouth, nose, and throat. Treatment is available if caught early. Those at highest risk are in the lowest socioeconomic status and those with malnutrition. Prevention includes vector control and surveillance to respond quickly to epidemics (World Health Organization, 2023b).
• Leprosy: a chronic bacterial infection of the skin and peripheral nerves. It is curable with multidrug therapy but if untreated it can cause progressive and permanent disability. Leprosy was reported in ancient civilizations, and prevalence has gradually declined in recent decades. In 2000, it was declared eliminated as a global health problem, although still present in over 100 countries. For prevention, the WHO recommends tracing household contacts and providing preventive drug treatment (World Health Organization, 2023f).
• Lymphatic Filariasis (“elephantiasis”): a parasitic infection spread by mosquitoes, leading to abnormal enlargement of body parts. This disease continues to cause suffering and hardship in 47 countries, although progress has been made in the last two decades. In 2000, the WHO started a campaign to eliminate this disease. They reported a 74% decrease by 2018. The treatment and prevention of Lymphatic Filariasis is accomplished through mass drug administration, providing preventive chemotherapy to millions of people. Aside from the drug treatment, vector control is also advised. Lymphatic Filariasis is considered eradicable by the ITFDE (World Health Organization, 2022f).
• Mycetoma, Chromoblastomycosis and other deep mycoses: chronic diseases causing growth of subcutaneous masses on extremities, often on the foot. The bacteria or fungus enters the body through minor trauma such as thorn pricks. Development of the disease is usually painless, and often remains unreported until it is advanced, when the only treatment is amputation. The only known prevention is to avoid walking barefoot and to avoid thorny bushes (World Health Organization, n.d.-c).
• Onchocerciasis (“river blindness”): parasitic disease transmitted by infected blackflies, which can lead to skin disfigurement and visual problems including blindness. Treatment and prevention are with mass drug administration of ivermectin (World Health Organization, 2022d).
• Rabies: a viral disease caused by a bite from an infected animal, usually a dog. Treatment after a bite requires a series of vaccinations. Rabies is a vaccine-preventable disease but is still prevalent in low income areas of Africa and Asia, where the required injections may be too expensive and less accessible. The most effective prevention is vaccination of domestic dogs. Education of children and adults about behavior of dogs and bite prevention is also recommended (World Health Organization, 2023e).
• Scabies and other Ectoparasites: parasitic infestations caused by mites that burrow into the skin and lay eggs, leading to a rash and intense itching. In tropical areas, scratching the primary skin rash can lead to more serious bacterial infections. Transmission is usually through close skin contact with an infected person. Treatment is with topical medication or oral ivermectin. In densely populated areas, everyone in the household may be treated at the same time, even if not yet symptomatic (World Health Organization, 2020b).
• Schistosomiasis: a parasitic disease transmitted in contaminated water and passed through human contact after re-contaminating the water by excreting the parasitic eggs. The best prevention is sanitation and access to clean water. WHO, and partners, are developing large-scale preemptive chemotherapy for high risk areas, especially for children and people who work in contaminated water, such as fishermen, farmers, and domestic workers (World Health Organization, 2023g).
• Soil-transmitted Helminthiases (“intestinal worms”): probably the most common infections worldwide, transmitted in soil contaminated by human feces. Light infestations are often asymptomatic but heavier infections may cause malnutrition in children, and other complications can be fatal. Treatments with inexpensive medications are available, and mass preventive chemotherapy is used in high risk areas. Sanitation and hygiene are the best preventive measures (World Health Organization, n.d.-f).
• Snakebite Envenoming: poisoning from snakebites, causing up to 138,000 deaths annually. Effective treatments exist but may not be accessible in remote and low income areas. Antivenom supplies are limited due to high production expenses and lack of data about the needs. WHO advocates more efforts to collaborate with partners for increased production and distribution of antivenom, and to educate the public about poisonous snakes (World Health Organization, 2021c).
• Taeniasis/Cysticercosis (“tapeworms”): intestinal parasite infection from eating undercooked and infected pork. The parasite can also be transmitted through contact with an infected person’s feces. If the infection reaches the brain (Neurocysticercosis), it can cause seizures, and is a common preventable cause of epilepsy, especially in areas where people live in close contact with pigs. Prevention measures include vaccination of pigs, sanitation, and health education about food safety and hygiene. Considered eradicable by the ITFDE (World Health Organization, 2022e).
• Trachoma: bacterial eye infection, often in preschool-aged children, spread by personal contact and by flies. Years of repeated infection may lead to permanent visual impairment. Trachoma is the leading infectious cause of  blindness worldwide. Treatment is with antibiotics, and surgery in advanced cases. Sanitation, clean water and hygiene provide the best prevention (World Health Organization, 2022h).
• Yaws: a chronic infectious disease of childhood, especially in tropical and rural areas, transmitted person-to-person. Initial lesions are wart-like tumors on the extremities that can lead to disfigurement. Treatment is with a single dose of azithromycin, an inexpensive antibiotic. No vaccine exists, but mass drug treatment is recommended for high-risk areas (World Health Organization, 2023c).

(World Health Organization, n.d.-d) (Tab 2)

The WHO estimates that over 1.7 billion of the world’s population should be targeted by prevention and treatment activities for at least one of these neglected tropical diseases each year.  

In addition to causing significant mortality and morbidity–approximately 200,000 deaths and 19 million disability adjusted life years (DALYs) lost annually–NTDs cost developing communities the equivalent of billions of United States dollars each year in direct health costs, loss of productivity, and reduced socioeconomic and educational attainment. They are also responsible for other consequences such as disability, stigmatization, social exclusion, and discrimination. NTDs also place considerable financial strain on patients and their families.

In spite of this, NTDs have historically ranked very low on and have been almost entirely absent from the global health agenda. They rightfully gained more recognition in 2015 with the Sustainable Development Goals (SDG target 3.3). SDG3 can be achieved only if the NTD goals are met. Because interventions to tackle NTDs are widely cross-sectoral, increasing their global prioritization can in fact catalyze progress to achieve all SDGs.

(World Health Organization, n.d.-d) (Tab 3)

WHO’s action to control, prevent, eliminate and eradicate NTDs is guided by the new NTD road map for 2021-2030, that moves away from vertical disease programmes to integrated cross-cutting approaches. The aim is to facilitate the coordinated scale-up of key interventions through public health approaches such as preventive chemotherapy, individual case management, vector control, veterinary public health, and water, sanitation and hygiene (WASH). 

The overarching 2030 global targets include a 90% reduction in the number of people requiring treatment for NTDs; a 75% reduction in DALYs related to NTDs; at least 100 countries eliminating at least one NTD; and the eradication of two diseases (dracunculiasis and yaws). 

Additional cross-cutting targets focus on integrated approaches, multisectoral coordination, universal health coverage and country ownership, while a further set of targets has been devised to measure progress against each disease (World Health Organization, 2023d).

Vaccines and immunization 

(World Health Organization, n.d.-h) (Tabs 1 & 2)

Immunization is a global health and development success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body’s natural defenses to build protection. When you get a vaccine, your immune system responds.

We now have vaccines to prevent more than 20 life-threatening diseases, helping people of all ages live longer, healthier lives. Immunization currently prevents 3.5-5 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza, and measles. “Yet, the World Health Organization (WHO) estimates that 1.5 million children under the age of 5 lose their lives to vaccine-preventable diseases every year” (The World Bank, n.d.).

Immunization is a key component of primary health care and an indisputable human right. It’s also one of the best health investments money can buy. Vaccines are also critical to the prevention and control of infectious disease outbreaks. They underpin global health security and will be a vital tool in the battle against antimicrobial resistance.

Vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.

Vaccines protect against many different diseases, including:

Immunization coverage 

(World Health Organization, 2022g)

Key facts

• - Only 25 vaccine introductions other than COVID-19 vaccine were reported in 2021.

• - Global coverage dropped from 86% in 2019 to 81% in 2021.

• - An estimated 25 million children under the age of 1 year did not receive basic vaccines, which is the highest number since 2009.

• - The number of girls not vaccinated against human papillomavirus (HPV) increased by 3.5 million, compared to 2019.

• - In 2021, the number of completely unvaccinated children increased by 5 million since 2019.

Overview

While immunization is one of the most successful public health interventions, coverage has plateaued over the last decade. The COVID-19 pandemic and associated disruptions have strained health systems, with 25 million children missing out on vaccination in 2021, 5.9 million more than in 2019 and the highest number since 2009.

During 2021, about 81% of infants worldwide (105 million infants) received 3 doses of diphtheria-tetanus-pertussis (DTP3) vaccine, protecting them against infectious diseases that can cause serious illness and disability or be fatal.

Twenty five vaccine introductions were reported in 2021 (not including COVID-19 vaccine introductions). Although this is an increase from 17 introductions in 2020, it is well below the number of introductions of any year in the past two decades prior to 2020. This slowdown is likely to continue as countries focus on ongoing efforts to control the COVID-19 pandemic.

A summary of global vaccination coverage in 2021 follows.

Haemophilus influenzae type b (Hib) causes meningitis and pneumonia. Hib vaccine had been introduced in 192 Member States by the end of 2021. Global coverage with 3 doses of Hib vaccine is estimated at 71%. Rates vary greatly between regions. The WHO Eastern Mediterranean Region and South-East Asia Region are each estimated to have 82% coverage, while it is only 29% in the WHO Western Pacific Region.

Hepatitis B is a viral infection that attacks the liver. Hepatitis B vaccine for infants had been introduced nationwide in 190 Member States by the end of 2021. Global coverage with 3 doses of hepatitis B vaccine is estimated at 80%. In addition, 111 Member States introduced nationwide 1 dose of hepatitis B vaccine to newborns within the first 24 hours of life. Global coverage is 42% and is as high as 78% in the WHO Western Pacific Region, while it is only estimated to be at 17% in the WHO African Region.

Human papillomavirus (HPV) is the most common viral infection of the reproductive tract and can cause cervical cancer in women, other types of cancer, and genital warts in both men and women. Including five new introductions, 116 Member States have introduced HPV vaccine by the end of 2021. Since many large countries have not yet introduced the vaccine and vaccine coverage decreased in 2021 in many countries, global coverage with the first dose of HPV among girls is now estimated at 15%. This is a proportionally large reduction from 20% in 2019.  

Meningitis A is an infection that is often deadly and leaves 1 in 5 affected individuals with long-term devastating sequelae. Before the introduction of MenAfriVac in 2010 – a revolutionary vaccine – meningitis serogroup A accounted for 80–85% of meningitis epidemics in the African meningitis belt. By the end of 2021, 350 million people in 24 out of the 26 countries in the meningitis belt had been vaccinated with MenAfriVac through campaigns. Thirteen countries had included MenAfriVac in their routine immunization schedule by 2021.

Measles is a highly contagious disease caused by a virus, which usually results in a high fever and rash, and can lead to blindness, encephalitis or death. By the end of 2021, 81% of children had received 1 dose of measles-containing vaccine by their second birthday, and 183 Member States had included a second dose as part of routine immunization and 71% of children received two doses of measles vaccine according to national immunization schedules.

Mumps is a highly contagious virus that causes painful swelling at the side of the face under the ears (the parotid glands), fever, headache and muscle aches. It can lead to viral meningitis. Mumps vaccine had been introduced nationwide in 123 Member States by the end of 2021.

Pneumococcal diseases include pneumonia, meningitis and febrile bacteraemia, as well as otitis media, sinusitis and bronchitis. Pneumococcal vaccine had been introduced in 154 Member States by the end of 2021, including 2 in some parts of the country, and global third dose coverage was estimated at 51%. Rates vary greatly between regions. The WHO European Region is estimated to have 82% coverage, while it is only 19% in the WHO Western Pacific Region.

Polio is a highly infectious viral disease that can cause irreversible paralysis. In 2021, 80% of infants around the world received three doses of polio vaccine. In 2021, the coverage of infants receiving their first dose of inactivated polio vaccine (IPV) in countries that are still using oral polio vaccine (OPV) is estimated at 79%. Targeted for global eradication, polio has been stopped in all countries except for Afghanistan and Pakistan. Until poliovirus transmission is interrupted in these countries, all countries remain at risk of importation of polio, especially vulnerable countries with weak public health and immunization services and travel or trade links to endemic countries.

Rotaviruses are the most common cause of severe diarrheal disease in young children throughout the world. Rotavirus vaccine was introduced in 118 countries by the end of 2021, including 2 in some parts of the country. Global coverage was estimated at 49%.

Rubella is a viral disease which is usually mild in children, but infection during early pregnancy may cause fetal death or congenital rubella syndrome, which can lead to defects of the brain, heart, eyes and ears. Rubella vaccine was introduced nationwide in 173 Member States by the end of 2021, and global coverage was estimated at 66%.

Tetanus is caused by a bacterium which grows in the absence of oxygen, for example in dirty wounds or the umbilical cord if it is not kept clean. The spores of C. tetani are present in the environment irrespective of geographical location. It produces a toxin which can cause serious complications or death. Maternal and neonatal tetanus persist as public health problems in 12 countries, mainly in Africa and Asia.

Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. As of 2021, yellow fever vaccine had been introduced in routine infant immunization programmes in 36 of the 40 countries and territories at risk for yellow fever in Africa and the Americas. In these 40 countries and territories, coverage is estimated at 47%.

Key challenges

In 2021, 18.2 million infants did not receive an initial dose of DTP vaccine, pointing to a lack of access to immunization and other health services, and an additional 6.8 million are partially vaccinated. Of the 25 million, more than 60% of these children live in 10 countries: Angola, Brazil, the Democratic Republic of the Congo, Ethiopia, India, Indonesia, Myanmar, Nigeria, Pakistan and the Philippines.

Monitoring data at subnational levels is critical to helping countries prioritize and tailor vaccination strategies and operational plans to address immunization gaps and reach every person with life-saving vaccines.

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World Health Organization. (2022f, March 16). Lymphatic filariasis. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis

World Health Organization. (2022g, July 14). Immunization coverage. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/immunization-coverage

World Health Organization. (2022h, October 5). Trachoma. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/trachoma

World Health Organization. (2022i, October 27). Tuberculosis. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/tuberculosis

World Health Organization. (2022j, November 9). HIV. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/hiv-aids

World Health Organization. (2022k, November 11). Pneumonia in children. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/pneumonia

World Health Organization. (2022l, December 8). Chikungunya. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/chikungunya

World Health Organization. (2022m, December 8). Malaria. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/malaria

World Health Organization. (2022n, December 8). World malaria report 2022. World Health Organization. https://www.who.int/publications-detail-redirect/9789240064898

World Health Organization. (2023a, January 12). Buruli ulcer (Mycobacterium ulcerans infection). World Health Organization. https://www.who.int/news-room/fact-sheets/detail/buruli-ulcer-(mycobacterium-ulcerans-infection)

World Health Organization. (2023b, January 12). Leishmaniasis. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/leishmaniasis

World Health Organization. (2023c, January 12). Yaws. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/yaws

World Health Organization. (2023d, January 16). Neglected tropical diseases Q&A. World Health Organization. https://www.who.int/news-room/questions-and-answers/item/neglected-tropical-diseases

World Health Organization. (2023e, January 19). Rabies. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/rabies

World Health Organization. (2023f, January 27). Leprosy. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/leprosy

World Health Organization. (2023g, February 1). Schistosomiasis. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/schistosomiasis