NAIROBI, Kenya Apr 26 – A global immunisation drive launched in response to pandemic-related setbacks has delivered more than 100 million vaccine doses to an estimated 18.3 million children across 36 countries, health agencies have announced.
The initiative, known as The Big Catch-Up, was rolled out during World Immunization Week in 2023 to address sharp declines in routine vaccinations caused by COVID-19 disruptions. It concluded in March 2026 and is on track to meet its target of reaching at least 21 million un- and under-immunised children.
According to Gavi, the Vaccine Alliance, the World Health Organization (WHO), and UNICEF, the programme reached children aged between one and five years, many of whom had missed routine immunisations in early childhood.
Of the 18.3 million children reached between 2023 and 2025, an estimated 12.3 million were “zero-dose” children who had never received a single vaccine, while 15 million had not been vaccinated against measles. The campaign also administered 23 million doses of inactivated polio vaccine (IPV), supporting global eradication efforts.
The 36 participating countries, largely in Africa and Asia, account for around 60 percent of zero-dose children worldwide. The initiative marked the first large-scale effort to systematically reach older children who had missed routine vaccines, expanding beyond the traditional focus on infants.
Several countries reported significant progress. Ethiopia reached more than 2.5 million previously unvaccinated children, while Nigeria delivered vaccines to about 2 million zero-dose children. A group of 12 countries, including Kenya, Tanzania, Zambia, Somalia and Pakistan, managed to reach more than 60 percent of children who had previously missed their first dose of routine vaccines.
Health agencies say the campaign has not only closed critical immunity gaps but also strengthened systems for identifying and reaching missed children. Governments trained health workers, updated eligibility policies, and worked closely with communities to improve uptake.
Despite the gains, agencies warn that the challenge is far from over.
In 2024 alone, an estimated 14.3 million infants globally did not receive a single vaccine through routine immunisation programmes. Many of these children live in fragile, conflict-affected or underserved communities, where access to healthcare remains limited.
“The Big Catch-Up shows what is possible when governments, partners and communities work together to reach the most vulnerable,” said Gavi CEO Dr Sania Nishtar, noting that millions of children are now protected against preventable diseases.
WHO Director-General Dr Tedros Adhanom Ghebreyesus said the programme helped reverse one of the most serious health impacts of the pandemic, while UNICEF Executive Director Catherine Russell emphasised the need to sustain progress through stronger routine immunisation systems.
Rising outbreaks of vaccine-preventable diseases underscore the urgency. Measles cases, for instance, have surged globally, with around 11 million reported in 2024, driven largely by gaps in vaccination coverage.
Health experts caution that large-scale catch-up campaigns are resource-intensive and should complement, not replace, routine immunisation. Sustained investment in healthcare systems, they say, remains the most effective way to protect children and prevent future outbreaks.
As countries mark World Immunization Week under the theme “For every generation, vaccines work,” global health partners are calling for renewed commitment to ensuring that every child—regardless of where they are born—has access to life-saving vaccines.