The Big Catch-Up: A Landmark Immunization Initiative
A multi-year effort launched in 2023 has delivered over 100 million vaccine doses to 18.3 million children across 36 countries, marking one of the largest coordinated catch-up campaigns in history.
Overview
The Big Catch-Up (BCU), launched during World Immunization Week 2023, is a joint initiative by Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF. The program has successfully reached an estimated 18.3 million children aged 1 to 5 across 36 countries, delivering more than 100 million vaccine doses to some of the world's most vulnerable populations.
Key Findings
- Of the 18.3 million children reached between 2023 and 2025, approximately 12.3 million were "zero-dose children" who had never received any vaccines.
- 15 million of these children had never received a measles vaccine, highlighting a critical gap in protection.
- The initiative provided 23 million doses of inactivated polio vaccine (IPV) to un- and under-vaccinated children.
- The program concluded on 31 March 2026 and is projected to meet its target of reaching at least 21 million un- and under-immunized children.
Geographic and Impact Distribution
The 36 participating countries—spanning Africa and Asia—account for 60% of all zero-dose children worldwide.
Twelve countries reported reaching more than 60% of all zero-dose children under 5 who had previously missed DTP1 (a key marker for immunization coverage):
Burkina Faso, Democratic People's Republic of Korea, Ethiopia, Kenya, Madagascar, Mauritania, Niger, Pakistan, Somalia, Togo, United Republic of Tanzania, and Zambia.
Notable country-level achievements include:
- Ethiopia reached over 2.5 million previously zero-dose children with DTP1, and delivered nearly 5 million doses of IPV and over 4 million doses of measles vaccine.
- Nigeria reached 2 million previously zero-dose children with DTP1 and administered 3.4 million IPV doses.
Systemic Improvements
The BCU initiative focused on building lasting systems to identify, screen, vaccinate, and monitor coverage rates in older children (ages 1 to 5). Countries updated age eligibility policies, trained health workers, and engaged communities to support catch-up efforts, creating a framework for sustainable immunization delivery.
Statements from Partner Organizations
Dr. Sania Nishtar, CEO of Gavi:
"The initiative demonstrates what is possible when governments, partners, and communities collaborate to protect the most vulnerable."
Dr. Tedros Adhanom Ghebreyesus, WHO Director-General:
"The success is a testament to health workers and national immunization programmes, now better equipped to find and vaccinate missed children."
Catherine Russell, UNICEF Executive Director:
"The gains must be sustained through investment in strong immunization systems, especially amid measles resurgence."
Challenges Ahead
Despite significant progress, an estimated 14.3 million infants under age one globally did not receive a single routine vaccine in 2024. Measles cases rose to approximately 11 million in 2024, and the number of countries facing large outbreaks has nearly tripled since 2021. Agencies emphasize that routine immunization remains the most sustainable approach to protecting future generations.
World Immunization Week 2026 Campaign
WHO, UNICEF, and Gavi are marking World Immunization Week (24–30 April 2026) with the campaign "For every generation, vaccines work," calling for sustained and expanded vaccination coverage at every age.