Global ''Big Catch-Up'' Initiative Reaches 18.3 Million Children with Over 100 Million Vaccine Doses, but Routine Immunization Gaps Persist
Introduction
A multi-year global vaccination campaign, the Big Catch-Up (BCU), has delivered more than 100 million vaccine doses to an estimated 18.3 million children aged one to five across 36 countries, primarily in Africa and Asia. The initiative, launched in April 2023 and concluded in March 2026, aimed to reverse declines in childhood immunization caused by the COVID-19 pandemic. According to Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF, the program is on track to meet its target of reaching at least 21 million un- or under-immunized children, though final data are still being compiled.
Main Body
The BCU was a coordinated response to pandemic-related disruptions that strained health systems and led to a resurgence of vaccine-preventable diseases such as measles and polio. Of the children reached between 2023 and 2025, approximately 12.3 million were classified as ''zero-dose''—having never received any vaccine—and 15 million had not previously received a measles vaccine. Additionally, 23 million doses of inactivated polio vaccine were administered to un- or under-vaccinated children. The 36 participating countries account for 60% of all zero-dose children globally, according to the agencies. The initiative focused on children aged one to five, a cohort that had aged out of routine infant immunization schedules. For the first time, the BCU systematically leveraged routine immunization systems to identify, screen, and vaccinate these older children. Participating countries updated age-eligibility policies, trained health workers, and engaged communities to support catch-up efforts. Twelve countries—including Burkina Faso, Ethiopia, Kenya, Niger, Pakistan, and Zambia—reported reaching more than 60% of zero-dose children under five who had missed the first dose of the diphtheria-tetanus-pertussis (DTP1) vaccine. Ethiopia alone 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. Despite these achievements, agencies emphasized that catch-up vaccination is a complementary measure, not a substitute for robust routine immunization. In 2024, an estimated 14.3 million infants worldwide failed to receive a single routine vaccine. The consequences are evident: measles outbreaks have risen in every region, with approximately 11 million cases recorded in 2024, and the number of countries experiencing large outbreaks has nearly tripled since 2021. The agencies attributed this surge to persistent gaps in routine measles vaccination, compounded by declining vaccine confidence in some previously high-coverage communities. Officials from the three organizations highlighted additional challenges. WHO vaccines director Kate O’Brien noted a growing politicization of vaccines and health. Gavi CEO Sania Nishtar stated that social media algorithms incentivize the promotion of disinformation, which she said requires strategic countermeasures. UNICEF’s global chief of immunization, Ephrem Lemango, observed that algorithms tend to reward outrage over accuracy and that anti-vaccine content has its own economy. Lemango also warned that recent sharp funding cuts to global health—including the U.S. decision to reduce financial support for Gavi, announced by Health Secretary Robert F. Kennedy Jr.—have seriously affected immunization service delivery and could reverse hard-earned progress.
Conclusion
The Big Catch-Up has demonstrated that targeted investment and political will can reduce immunization gaps among older children. However, the persistence of millions of infants missing routine vaccines each year, coupled with rising measles outbreaks, funding reductions, and the spread of vaccine misinformation, underscores the need for sustained domestic investment and reliable donor commitments. The agencies maintain that strengthening routine immunization systems remains the most effective and sustainable strategy for protecting children and preventing future outbreaks.