World Vaccination Week

World Immunization Week is a global public health initiative observed annually during the last week of April to raise awareness about the importance of vaccination. Throughout this week, the critical role of vaccination in protecting individual and community health is emphasized, and awareness campaigns are organized to increase vaccination rates. Led by the World Health Organization (WHO), World Immunization Week aims to improve access to vaccines and promote protection against vaccine-preventable diseases.

Historical Development of the Concept of Vaccination

Vaccination, or immunization, is one of the most effective methods developed to protect humanity from epidemic diseases, with its historical roots stretching back centuries. Before the 18th century, a method known as variolation was practiced in Asia and the Ottoman territories; it was an early form of immunity against smallpox, in which material taken from smallpox scabs was introduced into healthy individuals to induce a mild infection and confer protection. The modern concept of vaccination began at the end of the 18th century through the work of Edward Jenner. In 1796, Jenner discovered that infection with cowpox, a disease similar to smallpox that affected cattle, provided immunity against smallpox in humans, thereby developing the first vaccine.

This discovery marked a turning point in medical history, and the term “vaccine” (from the English vaccine, derived from the Latin vacca meaning cow) entered the literature in honor of Jenner’s work. In the 19th century, Louis Pasteur built upon Jenner’s findings and developed vaccines against diseases such as rabies and anthrax; in the first half of the 20th century, effective vaccines were also developed against diphtheria, tetanus, and pertussis (a respiratory infection). As vaccination techniques advanced and new vaccines were discovered for various diseases, many deadly illnesses were brought under control or eradicated entirely.

Purpose and History of World Immunization Week

World Immunization Week was launched by the WHO to highlight the global importance of immunization efforts and to bring attention to both achievements and gaps in this field. Historically, regional vaccination weeks evolved into a global initiative. In 2003, the Pan American Health Organization (PAHO) initiated “Vaccination Week” across the Americas; subsequently, other WHO regions including Europe, Africa, and the Eastern Mediterranean began organizing their own annual vaccination weeks. The idea of a unified global World Immunization Week was formally adopted by the World Health Assembly in 2012, and since then, the last week of April has been celebrated globally as World Immunization Week.

The core objective of this initiative is to expand access to immunization services against vaccine-preventable diseases worldwide, increase vaccine coverage, and raise public awareness about immunization. Each year, campaigns are organized around specific themes; for example, past themes such as “Closing the Immunization Gap” have emphasized the importance of vaccination. During this week, governments, health organizations, and civil society groups collaborate to conduct educational sessions, seminars, media campaigns, and free vaccination drives. Ultimately, World Immunization Week is a global mobilization effort that reminds the world of the life-saving impact of vaccination through international cooperation and strengthens community immunity.

Expanded Programme on Immunization (EPI) and Its Impact

One of the most significant steps in expanding vaccination globally was the launch of the Expanded Programme on Immunization (EPI) by the WHO in 1974. The program’s initial goal was to ensure that all children were vaccinated against six major childhood diseases: diphtheria, pertussis, tetanus, measles, polio, and tuberculosis (via the BCG vaccine). When EPI was implemented, vaccination coverage in developing countries was extremely low; in many nations, fewer than 5% of children received the necessary vaccines. Thanks to the program, immunization services rapidly expanded worldwide, particularly for essential childhood vaccines.

By the 1990s, global vaccination coverage had reached approximately 80% due to the impact of the Expanded Programme on Immunization. This increase protected millions of children from fatal diseases. It is estimated that vaccines prevent 3 to 5 million deaths worldwide each year. Over time, new vaccines were added to the EPI schedule; additional vaccines such as those for hepatitis B, Haemophilus influenzae type b (Hib), pneumococcus, and rubella were incorporated into many national immunization programs to protect children from these diseases.

One of EPI’s most remarkable achievements was the eradication of smallpox—the first disease in history to be eliminated globally. Through a coordinated global vaccination campaign, smallpox cases declined dramatically in the 1970s, and in 1980, the WHO declared smallpox eradicated from the planet. Similarly, polio cases have been reduced by more than 99% since 1988 thanks to EPI and the coordinated Global Polio Eradication Initiative.

Although polio remains endemic in some regions—particularly areas affected by conflict and poor access to healthcare—many countries have been declared polio-free, and global eradication is within reach. The widespread use of vaccines has also brought the incidence of measles, tetanus, and diphtheria to historically low levels. The Expanded Programme on Immunization has not only reduced disease cases but has also significantly lowered child mortality, contributing to increased life expectancy and improved overall public health.

Vaccine-Preventable Diseases

Vaccine-preventable diseases are infectious illnesses that either do not cause infection or result in mild symptoms when appropriate vaccines are administered, thereby preventing their spread within communities. Today, effective vaccines exist for numerous communicable diseases from infancy through adulthood. Examples include:

• Smallpox (Variola): Smallpox, one of the deadliest epidemics in history, has been completely eradicated worldwide through global vaccination campaigns. The smallpox virus no longer circulates among humans.

• Polio (Poliomyelitis): This disease, caused by the poliovirus and capable of inducing paralysis, has been largely controlled through vaccination. Polio cases are now absent in most parts of the world, with only a few countries reporting limited cases.

• Measles and Rubella: Measles, a highly contagious respiratory disease that can lead to severe complications, has reached elimination status in many countries due to widespread vaccination. Similarly, rubella and the congenital rubella syndrome it causes in unborn babies can also be prevented through vaccination.

• Diphtheria, Pertussis, and Tetanus: These three serious bacterial infections have been greatly reduced through the use of the pentavalent vaccine (DTaP—diphtheria, tetanus, and acellular pertussis), often combined with polio and Hib vaccines. Diphtheria and pertussis affect the respiratory tract and are particularly dangerous for children; tetanus enters the body through wounds and affects the nervous system, potentially leading to fatal outcomes including neonatal tetanus. Vaccination has made these diseases rare.

• Hepatitis B: The hepatitis B virus can cause chronic liver disease and liver cancer. Vaccination against it is included in national programs in many countries and is administered from birth, reducing the prevalence of hepatitis B carriers and transmission in the community.

• Haemophilus influenzae type b (Hib): The Hib vaccine, developed to protect against severe infections such as meningitis and pneumonia in children, has significantly reduced the incidence of these diseases in communities where it is used.

• Pneumococcus: Infections caused by Streptococcus pneumoniae—including pneumonia, meningitis, and bloodstream infections (sepsis)—can be severe, especially in young children and the elderly. The pneumococcal conjugate vaccine (PCV) has helped reduce child mortality and disability from these infections.

• Others: Additional vaccines such as rabies (a fatal disease transmitted through animal bites), the HPV vaccine (which prevents cervical cancer and other HPV-related diseases), varicella (chickenpox) vaccine, cholera vaccine, and yellow fever vaccine are also used regionally and globally to control these diseases.

These are only some of the vaccine-preventable diseases. Vaccines train the immune system to prevent disease upon actual exposure to pathogens or to make the illness milder. As a result, millions of people are protected from severe complications and death.

Herds Immunity (Community Immunity)

Herd immunity, also known as community immunity, occurs when a large proportion of a population is immune to a specific infectious disease, thereby indirectly protecting individuals who are not vaccinated or have not developed natural immunity. This concept is especially critical for highly contagious diseases. The percentage of the population that must be immune to prevent outbreaks depends on the disease’s transmissibility; for example, measles, which is extremely contagious, requires approximately 95% of the population to be vaccinated or immune, while less contagious diseases require lower thresholds.

When sufficient numbers of people are vaccinated, the spread of the microorganism within the community is interrupted, protecting those who cannot be vaccinated due to medical reasons, infants too young for vaccination, or those lacking access to vaccines. Herd immunity is a public health goal that aims not only for individual protection but also for safeguarding the most vulnerable members of society. Therefore, achieving high vaccination rates is critical. Herd immunity is also a prerequisite for eliminating or eradicating a disease. For instance, widespread vaccination and herd immunity played a pivotal role in the eradication of smallpox and the near-elimination of polio cases.

Vaccination Programs and Immunization in Türkiye

Türkiye is one of the countries with a long history of vaccination efforts. Vaccination activities date back to the Ottoman Empire, with the most notable milestone being the introduction of smallpox vaccination in the early 19th century. In the Ottoman territories, smallpox vaccination was tested shortly after 1800 and widely promoted under Sultan Mahmud II (1808–1839) for public use. Shortly after Pasteur’s discovery of the rabies vaccine in 1885, the Telkihhane-i Şahane (Dârülkelp) in Istanbul—the world’s third rabies vaccine center—was established in 1887, and rabies vaccine production began. Thus, modern vaccination practices were implemented early in Ottoman lands.

Preparation of a vaccine. (AA)

After the founding of the Republic of Türkiye, immunization programs remained a top public health priority. In the 1920s and 1930s, vaccination campaigns were conducted against smallpox, diphtheria, and typhoid; in 1930, the General Health Protection Law legally established the administration and monitoring of vaccines against infectious diseases. In the 1940s, BCG (tuberculosis) vaccination was introduced nationwide, and in the 1960s, polio vaccine was adopted. The 1970s marked a period of increased vaccine production and use in Türkiye, as well as the beginning of the impact of the WHO’s global EPI program. In 1981, Türkiye adopted the principles of the WHO’s Expanded Programme on Immunization and expanded its national immunization program, aiming to deliver six core childhood vaccines across the entire country through comprehensive campaigns led by the Ministry of Health.

The widespread and free provision of vaccination services in Türkiye has brought many infectious diseases under control. Smallpox has not been seen in Türkiye since the 1970s, as it was globally eradicated. Polio cases have not been detected since 1998 due to intensive vaccination campaigns; in 2002, Türkiye received certification from the WHO European Region as a polio-free country. Neonatal tetanus elimination programs, which focused on vaccinating pregnant women, were successful, and in 2009, Türkiye announced the elimination of neonatal tetanus. In the case of measles, large-scale vaccination campaigns between 2003 and 2005 dramatically reduced case numbers; thereafter, endemic transmission was interrupted, and only imported cases have been reported.

Since the 2000s, Türkiye has continued adding new vaccines to its immunization schedule. Hepatitis B and Haemophilus influenzae type b (Hib) vaccines were incorporated into routine schedules in 2006, followed by the pneumococcal vaccine in 2008. Rotavirus and HPV vaccines have also been introduced, initially for specific risk groups or pilot programs. Thanks to this expanded schedule, children in Türkiye now have free and widespread access to all core vaccines recommended by the World Health Organization. Vaccination coverage rates have remained high across Türkiye for many years; coverage for essential childhood vaccines in children under one year of age exceeds 95%. Thanks to these high rates, Türkiye has achieved or approached elimination targets for many regional diseases.

Although challenges such as occasional vaccine hesitancy and the spread of misinformation have emerged in recent years, health authorities and the scientific community are actively working to correct false information and maintain vaccination rates. Thanks to strong public trust in vaccination and the traditional societal acceptance of immunization programs, continuity in childhood vaccination has been preserved. Global initiatives such as World Immunization Week are also celebrated in Türkiye to raise public awareness about vaccines and strengthen social support for vaccinating future generations.

World Immunization Week is both a celebration and a reminder of humanity’s success in controlling countless deadly epidemics through vaccination. Through this week, the global achievements of immunization are highlighted, and international solidarity is encouraged to eliminate all vaccine-preventable diseases in the future.