A view shows The World Health Organization (WHO) headquarters in Geneva, Switzerland, 28 January 2025; Credit: REUTERS/Denis Balibouse

(Reuters) - More than 100 million vaccine doses have been delivered to 18.3 million children worldwide since 2023 under a global drive to reverse pandemic-related declines in childhood immunisation, the World Health Organization and vaccine alliance Gavi said on Thursday 23 April 2026.

The organisations had launched "The Big Catch-Up" during the World Immunisation Week in 2023. The initiative, focused on children aged one to five years and spanning 36 countries, concluded in March this year.

About 12.3 million children who were previously "zero-dose" and had never received a vaccine were immunized against diseases such as diphtheria and polio, the agencies said. Around 15 million children had not received a measles shot before the drive.

While final data is still being compiled, the global initiative is on track to meet its target of reaching at least 21 million un-immunised and under-immunised children, the agencies said.

The push comes at a time when some traditional backers such as the US are scaling back aid even as millions of infants still miss routine immunisation every year, leaving them vulnerable to preventable diseases such as measles, diphtheria and polio.

Ephrem Lemango, Chief of Immunization at UNICEF, said recent sharp funding cuts to global health have "seriously affected delivery of immunization services" and could "likely reverse hard earned progress".

Last year, US Health Secretary and long-time vaccine sceptic Robert F. Kennedy Jr. cut financial support for Gavi, a group that helps buy vaccines for the world's poorest countries. He claimed the group ignores safety issues with the immunisations it provides.

About 14.5 million children had missed basic vaccinations in 2023, with countries in the middle of global conflict seeing some of the sharpest setbacks.