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 vaccinating at least 21 million un- and under-immunized children.
However, agencies warn that while catch-up vaccination is an important strategy for closing immunization gaps, expanding the reach of routine immunization programmes remains the most effective and sustainable way to protect children against outbreaks of vaccine-preventable diseases.
Addressing the vaccine equity gap
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 per cent of all zero-dose worldwide. In these countries, pandemic-related immunization programme disruptions exacerbated this issue, and, 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 immunization 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 catalyzed 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 per cent 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.
