World Vaccination Week

World Vaccination Week is a public health initiative observed globally during the last week of April each year 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. World Health Organization (WHO) led World Vaccination Week aims to improve community access to vaccines and prevent vaccine-preventable diseases.

Vaccination (immunization) is one of the most effective methods developed to protect humanity from infectious diseases and its historical roots date back centuries. Before the 18th century, a method known as variolation was practiced in Asia and the Ottoman territories; this 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 with the work of Edward Jenner. In 1796, Jenner discovered that cowpox, a disease similar to smallpox that affected cattle, provided protection against smallpox in humans and developed the first vaccine.

This discovery marked a turning point in medical history, and the term “vaccine” (from English vaccine, derived from 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, pertussis (a respiratory, nasal, and throat infection). With the advancement of vaccination techniques and the discovery of vaccines against various diseases, many deadly illnesses have been brought under control or completely eradicated.

World Vaccination Week was launched by the WHO to highlight the global importance of vaccination efforts and bring attention to achievements and gaps in this field. Historically, vaccination weeks held in different regions evolved into a global initiative. Pan American Health Organization (PAHO) initiated “Vaccination Week” events across the Americas for the first time in 2003; 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 Vaccination Week was formally adopted in 2012 by a decision of the World Health Assembly, and since then, the last week of April has been celebrated as World Vaccination 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, World Vaccination Week features campaigns centered 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 organize educational events, seminars, media campaigns, and free vaccination drives. Ultimately, World Vaccination Week is a global mobilization effort that reminds the world of the life-saving impact of vaccination through international cooperation and strengthens community immunity.

One of the most significant steps in the global expansion of vaccination was the launch of the Expanded Programme on Immunization (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, poliomyelitis, and tuberculosis (via BCG vaccine). At the time of EPI’s implementation, vaccination rates in developing countries were extremely low; in many countries, fewer than 5% of children received the necessary vaccines. Thanks to the program, immunization services rapidly expanded worldwide, particularly for essential childhood vaccines.

Expanded Programme on Immunization’s impact led to global vaccination coverage reaching 80% by the 1990s. This increase protected millions of children from fatal diseases. It is estimated that vaccines prevent approximately 3 to 5 million deaths worldwide each year. Over the years, new vaccines have been added to the EPI schedule; additional vaccines such as Hepatitis B, Haemophilus influenzae type b (Hib), pneumococcal, and rubella vaccines have been 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), many countries have been declared free of the disease, and global eradication is within reach. The widespread use of vaccination has also brought the incidence of measles, tetanus, and diphtheria to historically low levels. Expanded Programme on Immunization has not only reduced disease cases but also significantly lowered child mortality, contributing to increased life expectancy and improved public health standards.

Vaccine-preventable diseases are illnesses that do not cause infection or severe illness in individuals when appropriate vaccines are administered, and whose transmission can be halted in the community. Today, effective vaccines exist against numerous infectious diseases from childhood through adulthood. Examples include:

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

• Poliomyelitis (Polio): This disease, caused by the poliovirus and capable of causing paralysis, has been largely controlled through vaccination. While polio cases are no longer detected in most parts of the world, only a few countries still report 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 use of the measles vaccine. Similarly, rubella and its associated congenital rubella syndrome in newborns are also preventable 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 vaccine, often combined with polio and Hib vaccines). Diphtheria and pertussis affect the respiratory tract and are particularly dangerous for children; tetanus enters 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, which can cause chronic liver disease and liver cancer, is now included in national immunization programs in many countries and is administered from birth. This has reduced the prevalence of Hepatitis B carriers and the spread of the disease in the population.

• Haemophilus influenzae type b (Hib): The Hib vaccine, developed against this bacterium that can cause 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 vaccine (PCV, pneumococcal conjugate vaccine) has reduced child mortality and disability rates by preventing these infections.

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

These are only some of the vaccine-preventable diseases. Vaccines work by training the body’s 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 serious complications and death caused by these diseases.

Herd immunity, also known as community immunity, is the condition in which 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 important in the context of communicable diseases. The percentage of immune individuals required to prevent an outbreak depends on the disease’s transmissibility. For example, for a highly contagious disease like measles, approximately 95% of the population must be vaccinated or immune, while for less contagious diseases, this threshold is lower.

When a sufficient proportion of the population is vaccinated, the spread of the microorganism is interrupted, protecting those who cannot be vaccinated due to medical reasons, infants below the vaccination age, or those lacking access to vaccines. Herd immunity is a public health goal that aims not only to protect individuals but also to safeguard the most vulnerable members of society. Therefore, achieving high vaccination rates is critical. Achieving herd immunity is also a prerequisite for eliminating or eradicating a disease. For instance, widespread vaccination of the population, or herd immunity, played a pivotal role in the eradication of smallpox and the near-elimination of polio cases.

Türkiye is one of the countries with a long history of vaccination efforts. Among the most notable vaccination activities dating back to the Ottoman Empire period is the introduction of the smallpox vaccine in the early 19th century. In the Ottoman territories, smallpox vaccination was tested immediately 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), the world’s third rabies vaccine center, was established in Istanbul in 1887, and rabies vaccine production began. Thus, modern vaccination practices were implemented early in Ottoman territories.

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After the founding of the Republic of Türkiye, immunization programs remained a top public health priority. In the 1920s and 1930s, vaccination campaigns against smallpox, diphtheria, and typhoid were conducted; in 1930, the General Health Protection Law legally established the implementation and monitoring of vaccines against infectious diseases. In the 1940s, BCG (tuberculosis) vaccination was rolled out nationwide, and in the 1960s, the polio vaccine was introduced. The 1970s marked a period of increased vaccine production and use in Türkiye, as well as the beginning of noticeable impact from 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. Under this initiative, the implementation of six core childhood vaccines was targeted across the entire country, and comprehensive vaccination campaigns were organized under the leadership of the Ministry of Health.

The widespread availability and free provision of vaccination services in Türkiye have brought many infectious diseases under control. Smallpox has not been observed in Türkiye since the 1970s, as it was globally. Poliomyelitis (polio) cases have not been detected since 1998 due to intensive vaccination campaigns, and in 2002, Türkiye received official 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. Measles cases dropped dramatically following large-scale vaccination campaigns conducted between 2003 and 2005; in subsequent years, endemic transmission of measles was interrupted, and only imported cases have been reported.

Since the 2000s, Türkiye has continued to add 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 and are administered to specific risk groups or within targeted programs. With this expanded schedule, children in Türkiye have universal and free access to all core vaccines recommended by the World Health Organization. Vaccination rates have remained high across Türkiye for many years; coverage for core childhood vaccines in children under one year of age is reported to exceed 95%. Thanks to these high rates, Türkiye has achieved or approached elimination targets for many regional diseases.

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

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