At the start of World Immunization Week 2026, global health agencies announced a major milestone in post-pandemic recovery efforts: the largest coordinated catch-up vaccination initiative has delivered over 100 million vaccine doses to an estimated 18.3 million children across 36 countries.
The initiative, known as The Massive Catch-Up, was launched during World Immunization Week 2023 as a response to significant declines in routine immunisation caused by disruptions to health services during the COVID-19 pandemic. Led by Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF, the programme targeted children who had missed critical vaccinations, with a focus on reaching those who had not received any vaccines at all.
According to the joint announcement, of the 18.3 million children reached between 2023 and 2025, an estimated 12.3 million were classified as “zero-dose” children — meaning they had not received a single vaccine dose prior to the initiative. 15 million of the children reached had never received a measles vaccine, highlighting persistent gaps in protection against one of the most contagious vaccine-preventable diseases.
The initiative also facilitated the administration of 23 million doses of inactivated polio vaccine (IPV) to under- and unvaccinated children, supporting global efforts toward polio eradication. Programme implementation concluded on 31 March 2026, with final data still being compiled at the time of the announcement.
Although the full dataset remains under review, officials stated that the initiative is on track to meet its original target of reaching at least 21 million under- or unimmunised children. This goal was established at the outset of the campaign as part of a broader strategy to recover immunisation progress lost during the pandemic.
Despite the progress, agency leaders cautioned that catch-up campaigns alone cannot sustain long-term protection. They emphasized that strengthening routine immunisation systems remains the most effective and sustainable approach to preventing outbreaks and ensuring equitable vaccine access.
“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,” said Dr Sania Nishtar, CEO of Gavi, the Vaccine Alliance. “Thanks to this accomplishment, not only are millions of children now protected from preventable diseases but so are their communities, for generations to reach.”
Dr Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization, highlighted the broader health system benefits: “By protecting children who missed out on vaccinations given that 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. The success of the Big Catch-Up is a testament to health workers and national immunisation programmes, which are now better equipped to find and vaccinate children missed by routine services.”
UNICEF Executive Director Catherine Russell echoed the call for sustained investment: “Vaccinations save lives. This initiative shows what’s possible when countries have the resources, tools, and political will to reach children with lifesaving vaccines. We’ve caught up with some of the children who missed routine vaccinations during the pandemic – but many more remain out of reach. The gains made through the Big Catch-Up must be sustained through investment in strong, reliable immunisation systems, especially at a time where measles is resurging.”
Beyond immediate catch-up efforts, the initiative sought to address deeper inequities in vaccine access. The 36 participating countries, primarily located in Africa and Asia, account for approximately 60% of the world’s zero-dose children. Pandemic-related disruptions worsened existing gaps in these regions, where many children already faced systemic barriers to healthcare.
To close these gaps, The Big Catch-Up introduced innovations in how immunisation services are delivered. For the first time on a large scale, countries systematically used existing routine immunisation infrastructure to reach older children aged 1 to 5 who had missed vaccines recommended before their first birthday. This included updating age eligibility policies, training health workers to identify and vaccinate missed children during routine visits, and engaging community leaders to build trust and encourage participation.
In several participating countries, the impact was particularly notable. Twelve nations — Burkina Faso, Democratic People’s Republic of Korea, Ethiopia, Kenya, Madagascar, Mauritania, Niger, Pakistan, Somalia, Togo, United Republic of Tanzania, and Zambia — reported reaching more than 60% of all zero-dose children under age five who had previously missed the first dose of diphtheria-tetanus-pertussis (DTP1) vaccine. In Ethiopia alone, over 2.5 million previously zero-dose children received DTP1, alongside nearly 5 million doses of IPV and more than 4 million doses of measles vaccine.
Outside this group, other countries also achieved significant reach. In Nigeria, for example, 2 million previously zero-dose children were vaccinated with DTP1, and 3.4 million doses of IPV were administered alongside millions of doses of other vaccines.
Even as the 36 focus countries received direct funding and technical support from Gavi, WHO, and UNICEF, the initiative also inspired similar catch-up activities in additional nations seeking to recover from pandemic-related declines in immunisation coverage.
Looking ahead, global health leaders noted that despite progress in catch-up efforts, the challenge of reaching infants remains substantial. In 2024, an estimated 14.3 million infants under one year of age globally did not receive a single vaccine through routine immunisation programmes — a figure that underscores the need for sustained investment in accessible, equitable health systems.
The consequences of persistent immunisation gaps are already visible. Measles cases have risen in every region, with approximately 11 million reported globally in 2024. The number of countries experiencing large measles outbreaks has nearly tripled since 2021, driven by uneven vaccine coverage and declining confidence in some communities.
Experts stress that while catch-up campaigns play a vital role in closing immunity gaps, they are intended as a temporary measure. Long-term protection depends on timely vaccination according to national immunisation schedules, which provides optimal and sustained defence against preventable diseases.
As part of World Immunization Week 2026, WHO, UNICEF, and Gavi launched a joint campaign under the theme “For every generation, vaccines work.” The initiative calls on governments to maintain and expand vaccine coverage across all age groups, with a continued focus on reaching zero-dose children and advancing equity in fragile and conflict-affected settings.
At the midpoint of the Immunisation Agenda 2030 and aligned with Gavi’s 2026–2030 strategy, the priority remains clear: closing the gap for the most underserved populations through durable investments in national immunisation programmes and sustained international support.
For updates on global immunisation efforts and upcoming initiatives, readers can refer to the official websites of Gavi, the World Health Organization, and UNICEF.
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