NAIROBI, Kenya, Apr 24— A global immunisation campaign spearheaded by the World Health Organization (WHO) has delivered more than 100 million doses of life-saving vaccines to children worldwide, marking the largest catch-up vaccination effort in history aimed at addressing declines triggered by the COVID-19 pandemic.
In a joint statement released at the start of World Immunization Week, WHO, the Gavi, the Vaccine Alliance, and the UNICEF said the multi-year Big Catch-Up (BCU) initiative reached an estimated 18.3 million children aged one to five across 36 countries between 2023 and 2025, helping to close dangerous immunity gaps created during the pandemic.
Of those reached, 12.3 million were so-called “zero-dose children” — children who had never received any routine vaccination — while 15 million had never received a measles vaccine, leaving them particularly vulnerable to outbreaks of preventable diseases.
“Programme implementation concluded on 31 March 2026. Although final data is still being compiled, the global initiative is forecast to be on track to meet its target of reaching at least 21 million un- and under-immunised children,” the joint statement said.
Health agencies said the initiative focused not only on pandemic recovery but also on addressing long-standing inequities in vaccine access, particularly in fragile, conflict-affected, and underserved communities.
The 36 participating countries across Africa and Asia account for about 60 percent of the world’s zero-dose children, a challenge worsened by disruptions to routine health services during the COVID-19 crisis.
For the first time, the Big Catch-Up programme systematically expanded routine immunisation systems to identify and vaccinate older children aged one to five who missed early vaccinations — a group often overlooked in traditional immunisation efforts.
Countries strengthened health systems by training workers to identify missed children during routine care, updating vaccine eligibility policies, and working with communities and civil society to boost awareness and participation in vaccination campaigns.
Twelve countries, including Kenya, Ethiopia, Somalia, Tanzania, Pakistan, and Zambia, reported reaching more than 60 percent of previously unvaccinated children under five who had missed their first dose of the diphtheria, tetanus and pertussis vaccine (DTP1).
“In Ethiopia, more than 2.5 million previously zero-dose children received DTP1,” the statement said.
“The country also delivered nearly 5 million doses of IPV and more than 4 million doses of measles vaccine, among other key vaccines, to un- and under-vaccinated children.”
Nigeria also recorded major gains, reaching about 2 million previously unvaccinated children with DTP1 and administering 3.4 million polio vaccine doses, among other immunisations.
Leaders hail historic achievement
Dr. Sania Nishtar, Chief Executive Officer of Gavi, described the initiative as a milestone in global health cooperation.
“As the largest-ever international effort to reach missed children with life-saving vaccines, the Big Catch-Up shows what is possible when governments, partners and communities work together to protect the most vulnerable in society,” she said.
WHO Director-General Dr. Tedros Adhanom Ghebreyesus said the campaign helped reverse one of the pandemic’s most damaging health consequences.
“By protecting children who missed out on vaccinations because of disruptions to health services caused by COVID-19, the Big Catch-Up has helped to undo one of the pandemic’s major negative consequences,” he said.
UNICEF Executive Director Catherine Russell warned that sustaining progress will require continued investment in routine immunisation systems, particularly as measles outbreaks rise globally.
“The gains made through the Big Catch-Up must be sustained through investment in strong, reliable immunisation systems, especially at a time when measles is resurging,” she said.
Despite the success of the campaign, health agencies cautioned that significant challenges remain.
In 2024, an estimated 14.3 million infants worldwide did not receive a single vaccine through routine immunisation programmes.
The consequences of these gaps are already visible. Measles cases surged to around 11 million globally in 2024, with the number of countries experiencing large outbreaks nearly tripling since 2021.
WHO, UNICEF, and Gavi are marking World Immunization Week 2026 under the theme “For every generation, vaccines work,” calling on governments and partners to sustain progress and ensure that all children, regardless of location, receive timely, life-saving vaccinations.