Massive ‘Big Catch-Up’ Initiative Delivers Over 100 Million Vaccines to Millions of Children Worldwide

A major global effort to reverse pandemic-era drops in childhood vaccination has successfully reached an estimated 18.3 million children across 36 countries with more than 100 million doses of life-saving vaccines, according to a joint announcement from Gavi, the Vaccine Alliance (Gavi), the World Health Organization (WHO), and UNICEF.

The initiative, known as The Big Catch-Up (BCU), was launched during World Immunization Week in 2023. It focused on children ages 1 to 5 who missed routine shots during the COVID-19 pandemic. Among those reached between 2023 and 2025, about 12.3 million were “zero-dose children” who had never received any vaccine before. Another 15 million had never gotten a measles vaccine.

The program also delivered 23 million doses of inactivated polio vaccine (IPV) to children who were either unvaccinated or under-vaccinated, a key step toward wiping out polio. The BCU wrapped up on March 31, 2026, and early data suggests it is on track to meet its goal of reaching at least 21 million children who had missed their shots.

Still, health leaders warn that catch-up campaigns alone are not enough. While these efforts help close dangerous gaps in protection, the best way to keep children safe and prevent disease outbreaks is to strengthen routine immunization programs that vaccinate infants on schedule every year.

Fighting the vaccine equity gap

The BCU did more than just recover from pandemic disruptions. It aimed to close the vaccine equity gap that leaves millions of children without essential shots before their first birthday. Most of these children live in fragile, conflict-affected, or underserved communities and often never get caught up as they grow older.

The 36 countries involved in the BCU—located across Africa and Asia—account for 60% of all zero-dose children worldwide. The pandemic made this problem worse by adding millions more children to the list of those already missing vaccines. To tackle this, the BCU went beyond infant immunization. For the first time, it systematically used routine immunization systems to reach older children—those between ages 1 and 5 who should have been vaccinated before turning one but were not.

Countries updated their policies to allow older children to get vaccinated. Health workers were trained to find, screen, and vaccinate missed children during routine visits. Communities and civil society groups also helped spread the word. By reaching millions of previously missed children and investing in better systems, the BCU made it easier for these countries to continue providing health and immunization services in the future.

Among the participating countries, 12 reported reaching more than 60% of all zero-dose children under age 5 who had previously missed their first dose of the DTP1 vaccine. These countries include Burkina Faso, Democratic People’s Republic of Korea, Ethiopia, Kenya, Madagascar, Mauritania, Niger, Pakistan, Somalia, Togo, United Republic of Tanzania, and Zambia.

In Ethiopia alone, more than 2.5 million zero-dose children received DTP1 for the first time. The country also gave out nearly 5 million doses of IPV and over 4 million doses of measles vaccine, among others. Nigeria also made big strides, reaching 2 million zero-dose children with DTP1 and administering 3.4 million doses of IPV.

While these 36 countries received Gavi funding and technical support from WHO and UNICEF, many other nations also worked to catch up missed children and rebuild immunization services after pandemic setbacks.

“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. “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, WHO Director-General. “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.”

Challenges remain

For the first time, the BCU successfully reached 12.3 million “older” zero-dose children between ages 1 and 5. But in 2024 alone, an estimated 14.3 million infants under age 1 worldwide still did not receive a single vaccine through routine programs. While the BCU shows progress is possible with leadership and investment, lowering that annual number will require building systems that consistently reach the hardest-to-reach communities. This challenge is made worse by rising birth rates, conflict and displacement, funding cuts, and strained health systems.

The results of these gaps are already visible. Measles outbreaks are increasing in every region, with around 11 million cases in 2024. The number of countries facing large outbreaks has nearly tripled since 2021. This surge is driven by ongoing gaps in measles vaccination through routine programs, along with declining vaccine confidence in some areas that once had high coverage.

Large catch-up campaigns like the BCU are resource-heavy and should only serve as a temporary fix. Getting children vaccinated on time, according to national schedules, remains the most effective and sustainable way to protect them and their communities.

For every generation, vaccines work

WHO, UNICEF, and Gavi, together with countries and communities, are marking World Immunization Week (April 24–30, 2026) with a joint campaign called “For every generation, vaccines work.” They are calling on countries to maintain and expand vaccination coverage at every age. As the world reaches the midpoint of the Immunisation Agenda 2030 (IA2030), and with Gavi’s new 2026–2030 strategy (Gavi 6.0) in place, the priority stays the same: reaching zero-dose children and improving equity in the hardest-to-reach communities, especially those dealing with conflict, instability, or weak health systems. Keeping this momentum going will require more long-term domestic investment in immunization programs and reliable commitments from partners and donors.