The Big Catch-Up (BCU), a landmark multi-year, multi-country effort to address declines in vaccinations caused by the massive COVID-19 pandemic, has reached an estimated 18.3 million children aged 1 to 5 years in 36 countries with more than 100 million doses of life-saving vaccines, helping close critical immunity gaps, as World Immunization Week kicks off The announcement was made by Gavi, the Vaccine Alliance (Gavi), WHO and UNICEF.
Of the 18.3 million children expected 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 unvaccinated and undervaccinated children, an essential intervention to reach polio eradication. Program implementation concludes on 31 March 2026. Although final data is still being compiled, estimates suggest the global initiative is on track to meet its goal of reaching at least 21 million unvaccinated and under-vaccinated children.
However, the agencies caution that while catch-up vaccination is an important strategy for closing the vaccination gap, expanding access to routine vaccination programs is the most effective and sustainable way to protect children and prevent outbreaks of vaccine-preventable diseases.
Addressing the Vaccine Equity Gap
In addition to pandemic recovery, the BCU initiative focused on closing the vaccine equity gap. Every year millions of children miss the required vaccinations before they turn one year old. Most of them live in fragile, conflict-affected, or underserved communities and as they grow up, they never catch up.
The 36 participating BCU countries in Africa and Asia currently contribute 60% of all zero-dose doses worldwide. Pandemic-related disruptions in vaccination schedules have exacerbated this problem, and, in these countries, have added millions of zero-dose children to those who have already missed vaccinations. To address this issue, the Big Catch-Up looked beyond infant vaccination, systematically leveraging routine immunization systems for the first time to delve deeper into the accumulated global group of older children aged 1 to 5 years – “older” because they should have received critical routine vaccinations before age 1 – who remain unprotected due to missed vaccinations.
BCU catalyzed long-standing systems for monitoring identification, screening, vaccination, and coverage rates of these older children – including updates to policies on age eligibility. Countries 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 vaccination access to millions of previously missed children and their communities and investing in systemic reforms, the BCU Drive makes it easier for countries to ensure that these populations, and others like them, continue to receive essential health and immunization services into the future.
Among 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 5 years of age who were previously missed by DTP1. In Ethiopia, more than 2.5 million first zero-dose children received DTP1. The country distributed nearly 5 million doses of IPV and more than 4 million doses of measles vaccine, in addition to other key vaccines, to unvaccinated and under-vaccinated children. A large number of children also reached countries outside this group. For example, in Nigeria, DTP1 was delivered to 2 million children in the first zero-dose, and 3.4 million doses of IPV were administered along with millions of doses of other vaccines.
While these 36 countries received Gavi funding and technical assistance from WHO and UNICEF through the BCU, many other countries also implemented activities during this period to catch up with missed children and accelerate efforts to restore vaccination services after pandemic-related backsliding.
“As the largest international effort ever to deliver life-saving vaccines to unreached children, 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 vaccine alliance Gavi. “Thanks to this achievement, not only are millions of children now protected from preventable diseases, but so are their communities for future generations.”
By protecting children who may have missed vaccinations due to disruption to health services due to COVID-19, Big Catch-Up has helped mitigate one of the major negative consequences of the pandemic. The success of the Big Catch-Up is a testament to health workers and national immunization programmes, who are now better equipped to find and vaccinate children missing out on routine services.”
Dr. Tedros Adhanom Ghebreyesus, Director-General, World Health Organization
“Vaccination saves lives,” said UNICEF Executive Director Catherine Russell. “This initiative shows what is possible when countries have the resources, equipment and political will to deliver life-saving vaccines to children. We have caught some of the children who missed routine vaccinations during the pandemic – but many children remain out of reach. The gains made through the Big Catch-Up must be sustained through investment in strong, reliable vaccination systems, especially at a time when measles is on the rise again.”
Considering the challenges ahead
Through the Big Catch-Up, for the first time, countries and global partners successfully reached 12.3 million “old” zero dose children aged 1 to 5 years. However, in 2024, an estimated 14.3 million infants under one year of age globally failed to receive a single vaccine through routine immunization programs. Despite BCU’s demonstration that progress is possible with leadership and targeted investment and support, reducing this annual number of missed babies will require building systems that consistently reach the hardest-hit communities – against a backdrop of growing birth cohorts, conflict and displacement, funding cuts and strained health systems.
The consequences of long-term delays in routine vaccination are clearly visible. For example, measles outbreaks are increasing in every region, with nearly 11 million cases in 2024, and the number of countries experiencing major outbreaks has nearly tripled since 2021. This increase is driven by persistent gaps in measles vaccination through routine vaccination programs, compounded by declining vaccine confidence in some already high-coverage communities.
Large-scale catch-up efforts are resource intensive and should serve only as a gap-filling measure that complements routine vaccination. Timely vaccination as per the National Immunization Program provides optimal protection and remains the most sustainable way to protect children and communities.
Vaccines work for every generation
WHO, UNICEF and Gavi, together 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 maintain and expand immunization coverage at every age. At the midpoint of the Immunization Agenda 2030 (IA2030), and at the heart of Gavi’s 2026-2030 strategy (Gavi 6.0), the priority remains the same: reaching children with zero doses and advancing equity in the hardest-to-reach communities, especially in countries struggling with conflict, instability or fragile health systems. Maintaining that momentum will require expanded long-term domestic investment in vaccination programs and credible commitments from partners and donors.
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