Big Catch-Up vaccination drive reaches 18M children, reversing pandemic immunity gaps

SWITZERLAND—Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF announced during World Immunisation Week that the Big Catch-Up (BCU) campaign has vaccinated 18.3 million children aged one to five across 36 countries.

Between 2023 and 2025, this multi-year initiative delivered over 100 million doses of life-saving vaccines to address severe immunization declines caused by the COVID-19 pandemic.

The campaign targeted some of the world’s most vulnerable populations.

Among the children reached, 12.3 million had never received any vaccine, while 15 million had never been immunized against measles.

The initiative also administered 23 million doses of inactivated polio vaccine (IPV) to unvaccinated and under-vaccinated children, supporting global polio eradication efforts.

Programme implementation concluded on March 31, 2026, with the global initiative on track to exceed its target of reaching at least 21 million under-immunised children.

Closing the global immunity gap

The 36 participating countries in Africa and Asia account for 60 percent of all zero-dose children worldwide—children who have never received any vaccination.

These nations face compounding challenges from pandemic disruptions, fragile health systems, and limited resources.

The BCU took an unprecedented approach by systematically identifying and vaccinating older children aged one to five who should have received routine vaccines before their first birthday but had been missed by standard immunization programs.

Countries implemented comprehensive strategies to reach these vulnerable populations.

Health workers received training to identify and screen for missed children during routine care, while policymakers updated age-eligibility guidelines.

Communities and civil society organizations supported catch-up efforts through engagement and outreach.

These systemic improvements created lasting infrastructure to monitor coverage and prevent future gaps.

The results proved substantial. Twelve countries reported reaching over 60 percent of zero-dose children under five who had missed diphtheria, tetanus, and pertussis (DTP1) vaccines.

Ethiopia led with remarkable achievements, vaccinating 2.5 million previously zero-dose children with DTP1 and delivering nearly 5 million IPV doses and 4 million measles vaccine doses.

Nigeria reached 2 million zero-dose children with DTP1 while administering 3.4 million IPV doses alongside other critical vaccines.

Strengthening immunization systems for the future

Agency leaders emphasized that while catch-up campaigns prove essential for addressing accumulated gaps, sustaining progress requires strong routine immunization programs.

Dr. Sania Nishtar, CEO of Gavi, noted that the initiative protected millions of children and their entire communities for generations.

WHO Director-General Dr. Tedros Adhanom Ghebreyesus credited health workers and national immunisation programmes now better equipped to find missed children.

UNICEF Executive Director Catherine Russell highlighted ongoing challenges, noting that in 2024, an estimated 14.3 million infants under one year old failed to receive any vaccine through routine programs globally.

Measles outbreaks are rising across every region, with around 11 million cases recorded in 2024, driven by persistent vaccination gaps and declining vaccine confidence in previously high-coverage areas.

The number of countries facing large measles outbreaks has nearly tripled since 2021.

Agencies warn that while catch-up efforts fill critical gaps, timely vaccination according to national schedules remains the most sustainable path forward.

Building resilient immunization systems continues to be essential for protecting future generations against vaccine-preventable diseases.