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Agartala, Tripura
The Big Catch-Up (BCU), a historic multi-year, multi-country effort to address vaccination declines driven largely by the COVID-19 pandemic, has reached an estimated 18.3 million children aged 1 to 5 across 36 countries with more than 100 million doses of life-saving vaccines, helping to narrow critical immunity gaps, announced Gavi, the Vaccine Alliance (Gavi), WHO, and UNICEF at the start of World Immunization Week.
Of the 18.3 million children reached between 2023 and 2025, an estimated 12.3 million were “zero-dose children” who had not yet received a vaccine and 15 million had never received a measles vaccine. BCU also provided 23 million doses of inactivated polio vaccine (IPV) to un- and under-vaccinated children, an essential intervention to reach polio eradication. Programme implementation concluded on 31 March 2026. Although final data is still being compiled, the global initiative is forecasted to be on track to meet its target of reaching at least 21 million un- and under-immunized children.
However, agencies warn that while catch-up vaccination is an important strategy for closing immunisation gaps, expanding the reach of routine immunization programmes remains the most effective and sustainable way to protect children and prevent outbreaks of vaccine-preventable diseases.
Beyond pandemic recovery, the BCU initiative focused on closing the vaccine equity gap. Millions of children every year miss the essential vaccinations they should receive before the age of one. Most of them live in fragile, conflict-affected, or underserved communities and are never caught up as they grow older.
The 36 participating BCU countries across Africa and Asia currently account for 60% of all zero-dose worldwide. Pandemic-related immunisation programme disruptions exacerbated this issue, and, in these countries, added millions more zero-dose children to those who already chronically miss out. To address this issue, the Big Catch-Up looked beyond infant immunization, for the first-time ever systematically leveraging routine immunisation systems to make deep inroads into the accumulated global cohort of older children between the ages of 1 to 5 – “older” because they should have received critical routine vaccines before the age of 1 – who remain vulnerable due to missed vaccinations.
BCU catalysed long-lasting systems to identify, screen, vaccinate and monitor coverage rates in these older children – including updates to policies on age eligibility. Countries also oriented and trained health workers to identify, screen and vaccinate missed children as part of routine care and engaged with communities and civil society to support catch-up efforts. By expanding the reach of immunization to millions of previously missed children and their communities, and investing in systemic improvements, the BCU drive has made it easier for the countries to ensure these populations and others like them continue to receive essential health and immunization services in the future.
Among the participating countries, 12 countries (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 the age of 5 who had previously missed DTP1. In Ethiopia, more than 2.5 million previously zero-dose children received DTP1. 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. Countries outside this group also reached large numbers of children. In Nigeria, for example, 2 million previously zero-dose children were reached with DTP1, and 3.4 million doses of IPV were administered alongside millions of doses of other vaccines.
While these 36 countries received Gavi funding and technical assistance from WHO and UNICEF through BCU, many other countries also implemented activities during this period to accelerate efforts to catch-up missed children and recover immunisation services following pandemic-related backsliding.
“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 come.”
"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," said Dr Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization. “The success of the Big Catch-Up is a testament to health workers and national immunization programmes, which are now better equipped to find and vaccinate children missed by routine services."
"Vaccinations save lives,” said UNICEF Executive Director Catherine Russell. “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."
Through the Big Catch-Up, for the first time ever, countries and global partners successfully reached 12.3 million “older” zero dose children between the ages of 1 to 5. However, in 2024, an estimated 14.3 million infants under the age of one globally failed to receive a single vaccine through routine immunization programmes. Despite BCU demonstrating progress is possible with leadership and targeted investment and support, lowering this annual number of infants who miss out will require building systems that consistently reach the hardest to reach communities – against a backdrop of rising birth cohorts, conflict and displacement, funding cuts, and strained health systems.
The consequences of chronic gaps in routine immunisation are plain to see. Measles outbreaks, for example, are rising in every region with around 11 million cases in 2024, and the number of countries facing large outbreaks has almost tripled since 2021. This surge is driven by persistent gaps in measles vaccination through routine immunization programmes, compounded by declining vaccine confidence in some previously high-coverage communities.
Large-scale catch-up efforts are resource intensive and should serve only as a gap-filling measure that is complementary to routine immunization. Timely vaccination according to national immunisation schedules provides optimal protection and continues to be the most sustainable way to safeguard children and communities.
WHO, UNICEF, and Gavi, along with countries and communities, are marking World Immunization Week (24–30 April 2026) with a joint campaign, "For every generation, vaccines work," calling on countries to sustain and expand vaccination coverage at every age. At the midpoint of the Immunisation Agenda 2030 (IA2030), and central to Gavi's 2026–2030 strategy (Gavi 6.0), the priority remains the same: reaching zero-dose children and advancing equity in the hardest-to-reach communities, particularly in countries grappling with conflict, instability, or fragile health systems. Maintaining that momentum will require expanding long-term domestic investments in immunization programmes and reliable commitments from partners and donors.
