The Big Catch-Up, launched during World Immunization Week 2023, has delivered over 100 million vaccine doses to approximately 18.3 million children across 36 countries, according to Gavi, WHO, and UNICEF. The multi-year global initiative was designed to recover immunization coverage lost during the COVID-19 pandemic and has focused on reaching children who had missed essential vaccines. Of those reached, around 12.3 million were “zero-dose” children who had never received any vaccines, while about 15 million had not received protection against measles. The programme also delivered millions of doses of inactivated polio and other essential vaccines, and is on track to meet its target of reaching 21 million un- and under-immunized children when it concluded in March 2026.
The initiative primarily targeted countries in Africa and Asia, which together account for the majority of zero-dose children globally. It not only focused on infants but also extended efforts to older children aged one to five who had missed routine vaccinations earlier in life. Health systems were strengthened through improved tracking, screening, and outreach mechanisms, along with updated policies and training for health workers. Community engagement also played a key role in identifying and vaccinating missed children, helping integrate catch-up efforts into routine immunization systems.
Several countries reported significant progress, with some reaching more than 60% of zero-dose children under five. Large-scale vaccination drives in countries such as Ethiopia and Nigeria helped deliver millions of doses across multiple vaccines, including those for measles and polio. While the Big Catch-Up was supported by Gavi with technical assistance from WHO and UNICEF, many other countries also implemented similar recovery efforts independently to restore disrupted immunization services.
Global health leaders have described the initiative as a major achievement in reducing immunity gaps and preventing outbreaks of vaccine-preventable diseases. However, they caution that catch-up campaigns alone are not enough to ensure long-term protection. Routine immunization remains the most effective and sustainable approach to safeguarding children, especially as millions of infants still miss basic vaccines each year due to gaps in healthcare access.
Despite the progress made, challenges remain significant. In 2024 alone, an estimated 14.3 million infants globally did not receive a single vaccine dose, and measles cases have surged worldwide, driven by declining coverage and weak health systems in some regions. Health agencies stress that sustained investment, stronger immunization systems, and improved access in fragile and underserved communities are essential to prevent future outbreaks and maintain the gains achieved through the Big Catch-Up initiative.
