On April 24, 2026, the World Health Organization (WHO), UNICEF, and Gavi, the Vaccine Alliance, announced that their joint “Big Catch-Up” initiative had successfully administered over 100 million doses of childhood vaccines to approximately 18.3 million children aged 1 to 5 years across 36 countries. The campaign, launched in 2023 during World Immunization Week, aimed to reverse the decline in routine immunization caused by disruptions during the COVID-19 pandemic.
According to verified reports from WHO and partner agencies, of the 18.3 million children reached, an estimated 12.3 million were “zero-dose” children who had never received any vaccine prior to the initiative. 15 million children in the target group had not previously received the measles vaccine. The effort too included the administration of 23 million doses of inactivated poliovirus vaccine to children who were either unvaccinated or had incomplete polio immunization schedules.
The initiative focused on 36 countries identified as having 60% of the world’s unvaccinated children, primarily in Africa and Asia. Gavi’s CEO, Sania Nishtar, stated that the number of doses delivered equated to vaccinating every child under five in the European Union five times over. She emphasized that the campaign not only protected millions of children but also strengthened health systems through investments in data systems, service delivery models, and community outreach.
Despite progress, officials warned that the number of infants missing out on life-saving vaccines through routine immunization remains high each year. The initiative concluded in March 2026 and is on track to meet its goal of reaching 21 million children. WHO, UNICEF, and Gavi continue to urge sustained investment in immunization programs to prevent future outbreaks of vaccine-preventable diseases.
Understanding the Impact of Pandemic-Related Immunization Gaps
The COVID-19 pandemic disrupted routine healthcare services globally, leading to millions of children missing critical vaccine doses. Lockdowns, redirected health resources, and fear of infection contributed to declining vaccination rates in many low- and middle-income countries. Before the pandemic, global coverage for basic vaccines like DTP3 (diphtheria, tetanus, pertussis) had stalled around 86%, but dropped significantly in 2020 and 2021, leaving millions of children vulnerable to diseases such as measles, polio, and pneumonia.
The “Big Catch-Up” initiative was designed as a targeted response to this backlog. Rather than relying solely on routine services, it employed intensified outreach, mobile clinics, and community health workers to locate and vaccinate children who had fallen through the cracks. The effort was coordinated nationally but supported globally through funding and technical assistance from Gavi, WHO, and UNICEF.
Measles, in particular, poses a high risk when vaccination rates fall. The virus is highly contagious, and outbreaks can occur quickly in under-immunized populations. By ensuring that 15 million children received the measles vaccine for the first time, the initiative helped close a critical immunity gap. Similarly, the polio component remains vital as the world nears eradication; any lapse in immunization could allow the virus to resurge.
How the Initiative Was Implemented on the Ground
In participating countries, ministries of health led the implementation with support from local partners. Strategies included integrating catch-up vaccination into existing health visits, conducting door-to-door campaigns in remote areas, and using electronic registries to track defaulters. In some regions, traditional leaders and religious figures were engaged to build trust and encourage vaccine acceptance.
Cold chain logistics were strengthened to ensure vaccine potency, especially in areas with limited infrastructure. Solar-powered refrigerators and real-time temperature monitoring devices were deployed in clinics and outreach sites. Training programs were expanded for health workers to manage increased workloads and address vaccine hesitancy through empathetic communication.
Data collection played a key role in measuring progress. Countries used digital tools to monitor coverage in real time, allowing for rapid adjustments to underperforming areas. This focus on accountability helped ensure that resources were directed where they were needed most.
What This Means for Global Health Security
Experts stress that while emergency catch-up campaigns are essential, they are not a substitute for strong, resilient routine immunization systems. The experience of the pandemic revealed how quickly gains can be lost when health systems face shock. Investments made during the “Big Catch-Up” — such as improved data systems, supply chain upgrades, and community engagement frameworks — are intended to have lasting benefits beyond the campaign’s end.
Gavi has indicated that future funding will prioritize strengthening routine immunization alongside outbreak response. The goal is to build systems capable of maintaining high coverage even during crises. For families, this means more reliable access to vaccines at local clinics, reducing the require for large-scale emergency interventions.
As of April 2026, WHO and UNICEF continue to monitor global immunization trends through the Joint Reporting Form and regional surveillance networks. The next major data release is expected during World Immunization Week in April 2027, which will provide updated estimates on routine coverage and progress toward the Immunization Agenda 2030 targets.
Parents and caregivers seeking information about childhood vaccines are encouraged to consult national health ministry websites or visit the WHO immunization portal for updated schedules and safety guidance. Community health workers remain a vital source of trusted information, especially in underserved areas.
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