Massive Vaccine Drive Reaches 18.3 Million Children with Over 100 Million Shots

The Big Catch-Up (BCU), a global effort launched during World Immunization Week 2023 to reverse pandemic-era vaccination declines, has delivered more than 100 million doses of life-saving vaccines to an estimated 18.3 million children aged 1 to 5 in 36 countries, according to Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF.

Among the children 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 initiative also gave 23 million doses of inactivated polio vaccine (IPV) to children who were unvaccinated or under-vaccinated, a key step toward eradicating polio.

The program wrapped up on March 31, 2026. While final numbers are still being collected, the initiative is expected to meet its goal of reaching at least 21 million children who missed routine shots.

Still, health agencies warn that catch-up drives alone aren’t enough. Expanding routine immunization programs remains the best way to protect children and prevent outbreaks of preventable diseases.

Closing the vaccine equity gap

The BCU aimed to fix a long-standing problem: millions of children worldwide miss essential vaccines before their first birthday. Most live in fragile, conflict-ridden, or underserved areas and never get caught up as they grow older.

The 36 countries involved—mostly in Africa and Asia—account for 60% of all zero-dose children globally. The pandemic made things worse, adding millions more to the list. To tackle this, the BCU did something new: it used routine immunization systems to reach older children aged 1 to 5 who had missed their shots. These kids were “older” because they should have been vaccinated before turning 1.

The program helped countries build lasting systems to find, screen, and vaccinate these children. It also updated age rules for vaccines, trained health workers, and worked with communities to support catch-up efforts. This made it easier for countries to keep providing care to these groups in the future.

Twelve countries—including Burkina Faso, Ethiopia, Kenya, Niger, Pakistan, Somalia, and Zambia—reported reaching more than 60% of their zero-dose children under 5 who had missed the first dose of the DTP vaccine. In Ethiopia alone, more than 2.5 million previously zero-dose kids got their first DTP shot. The country also gave nearly 5 million doses of IPV and over 4 million measles vaccine doses. In Nigeria, 2 million zero-dose children received DTP1, and 3.4 million IPV doses were given, along with millions of other vaccines.

While these 36 countries got Gavi funding and technical help from WHO and UNICEF, many other nations also ran their own catch-up efforts during this time.

“The Big Catch-Up shows what’s possible when governments, partners, and communities work together to protect the most vulnerable,” said Dr. Sania Nishtar, CEO of Gavi. “Thanks to this achievement, millions of children—and their communities—are now protected from preventable diseases for generations to come.”

Dr. Tedros Adhanom Ghebreyesus, WHO Director-General, added: “By protecting children who missed vaccinations due to COVID-19 disruptions, the Big Catch-Up has helped undo one of the pandemic’s major harms. This success is a testament to health workers and national immunization programs, which are now better at finding and vaccinating children missed by routine services.”

UNICEF Executive Director Catherine Russell said: “Vaccinations save lives. This initiative shows what’s possible when countries have the resources, tools, and political will. We’ve caught up with some children who missed routine shots during the pandemic—but many more remain out of reach. The gains must be sustained through investment in strong immunization systems, especially as measles makes a comeback.”

Challenges ahead

For the first time, the BCU successfully reached 12.3 million “older” zero-dose children aged 1 to 5. Yet in 2024, an estimated 14.3 million infants under 1 worldwide still didn’t get a single vaccine through routine programs. Lowering that number will require building systems that consistently reach the hardest-to-reach communities, even as birth rates rise, conflicts and displacement grow, funding shrinks, and health systems struggle.

The results of these gaps are clear. Measles outbreaks are rising everywhere, with about 11 million cases in 2024. The number of countries facing large outbreaks has nearly tripled since 2021. This surge is driven by missed measles vaccines through routine programs, plus falling vaccine confidence in some areas that used to have high coverage.

Large catch-up efforts take a lot of resources and should only serve as a temporary fix. Getting vaccines on time according to national schedules offers the best protection and remains the most sustainable way to keep children and communities safe.

For every generation, vaccines work

WHO, UNICEF, and Gavi are marking World Immunization Week (April 24–30, 2026) with a joint campaign called “For every generation, vaccines work.” They’re urging countries to keep expanding vaccination coverage at every age. At the midpoint of the Immunization Agenda 2030 and central to Gavi’s 2026–2030 strategy, the priority stays the same: reaching zero-dose children and advancing equity in the hardest-to-reach communities, especially those facing conflict, instability, or weak health systems. Keeping that momentum will require more long-term domestic investment in immunization programs and reliable commitments from partners and donors.