GENEVA/NEW YORK – As the world marks World Immunization Week 2026, global health authorities have unveiled the results of a historic, multi-year intervention designed to reverse the devastating impact of COVID-19 on global health infrastructure. Known as "The Big Catch-Up" (BCU), the initiative has successfully reached 18.3 million children aged one to five across 36 nations with over 100 million doses of life-saving vaccines.
This monumental effort, spearheaded by Gavi, the Vaccine Alliance (Gavi), the World Health Organization (WHO), and UNICEF, represents the largest-ever international attempt to close critical immunity gaps. While the program officially concluded its implementation phase on March 31, 2026, its legacy is already being heralded as a turning point in global health equity.
The Main Facts: A Global Safety Net
The Big Catch-Up was launched in response to a precipitous decline in childhood immunization coverage during the pandemic years. Between 2023 and 2026, the initiative focused on identifying "zero-dose" children—those who had never received a single routine vaccination—and providing them with essential protections against diseases such as diphtheria, tetanus, pertussis, and measles.
Of the 18.3 million children reached, approximately 12.3 million were previously classified as zero-dose children. Furthermore, 15 million children received their first-ever measles vaccine, and 23 million received the inactivated polio vaccine (IPV). Although final data collection remains ongoing, the initiative is currently on track to hit its ambitious target of 21 million children reached, a milestone that serves as a testament to the resilience of global health systems.
A Chronology of the Crisis and Response
The Pandemic Backslide (2020–2022)
The origins of the BCU are rooted in the massive disruptions caused by COVID-19. Lockdowns, supply chain collapses, and the redirection of health workers toward pandemic response led to the largest sustained decline in childhood vaccinations in 30 years. Millions of children in fragile and conflict-affected regions were left vulnerable, creating a "immunity debt" that threatened to trigger mass outbreaks of preventable diseases.
The Launch of BCU (2023)
Recognizing that these children would not naturally "catch up" without targeted intervention, Gavi, WHO, and UNICEF launched the Big Catch-Up. The strategy was unique: it moved beyond standard infant-only immunization models to systematically target the "older" cohort—children aged one to five who had missed their infant shots due to the pandemic.
Operational Phase (2023–2026)
For three years, participating countries underwent a radical restructuring of their immunization services. This included:
- Policy Reform: Updating age-eligibility criteria to ensure children up to five could still receive routine vaccines.
- Training: Upskilling thousands of health workers to conduct outreach in hard-to-reach communities.
- Systems Strengthening: Integrating vaccination screening into routine primary healthcare visits, rather than relying solely on vertical, standalone programs.
The Close of Implementation (March 2026)
As of March 31, 2026, the primary implementation phase has concluded. The focus has now shifted to integrating these new, more resilient immunization pathways into national health budgets, ensuring the gains made during the BCU are not lost.
Supporting Data: By the Numbers
The success of the BCU is not merely a global statistic; it is a story of regional breakthroughs. The 36 countries involved—primarily across Africa and Asia—account for 60% of the world’s zero-dose population.
Regional Success Stories
- Ethiopia: The country stands as a beacon of progress, having reached more than 2.5 million zero-dose children with the DTP1 vaccine. Additionally, Ethiopia successfully administered nearly 5 million doses of IPV and 4 million measles vaccines.
- Nigeria: In a massive logistical undertaking, Nigeria reached 2 million previously zero-dose children with DTP1 and administered 3.4 million doses of IPV, effectively shielding a vast number of children from polio.
- Broad Impact: Across the 36 participating nations, 12 countries—including Burkina Faso, Kenya, Madagascar, Mauritania, Niger, Pakistan, Somalia, Togo, Tanzania, and Zambia—reported that they had reached more than 60% of all zero-dose children under the age of five who had previously missed their first DTP1 dose.
Official Responses: A United Front
The leadership of the partner organizations emphasized that the success of the BCU is not just about the numbers, but about the precedent it sets for future crisis response.
Dr. Sania Nishtar, CEO of Gavi, the Vaccine Alliance:
"As the largest ever international effort to reach missed children with life-saving vaccines, the Big Catch-Up shows what is possible when governments, partners, and communities work together to protect the most vulnerable in society. Thanks to this accomplishment, not only are millions of children now protected from preventable diseases, but so are their communities, for generations to come."
Dr. Tedros Adhanom Ghebreyesus, Director-General of the WHO:
"By protecting children who missed out on vaccinations because of disruptions to health services caused by COVID-19, the Big Catch-Up has helped to undo one of the pandemic’s major negative consequences. The success of the Big Catch-Up is a testament to health workers and national immunization programmes, which are now better equipped to find and vaccinate children missed by routine services."
Catherine Russell, Executive Director of UNICEF:
"Vaccinations save lives. This initiative shows what’s possible when countries have the resources, tools, and political will to reach children with life-saving vaccines. We’ve caught up with some of the children who missed routine vaccinations during the pandemic—but many more remain out of reach. The gains made through the Big Catch-Up must be sustained through investment in strong, reliable immunization systems, especially at a time where measles is resurging."
Implications: The Road Ahead
Despite the triumphs of the BCU, the agencies warn that the global immunization landscape remains fragile.
The Persistence of the Zero-Dose Challenge
Even as the BCU closes, the numbers remain sobering. In 2024 alone, an estimated 14.3 million infants globally failed to receive a single vaccine through routine programs. This persistent gap is driven by a "perfect storm" of rising birth cohorts, escalating conflict, displacement, and economic instability that has led to funding cuts in national health programs.
The Measles Resurgence
The most immediate consequence of these chronic gaps is the return of measles. In 2024, the world saw 11 million cases of measles, with the number of countries experiencing large-scale outbreaks tripling since 2021. Experts attribute this to a combination of gaps in routine immunization and a dangerous decline in vaccine confidence, which has allowed the virus to find footholds in communities that previously maintained high coverage.
From "Catch-Up" to "Sustainability"
The primary lesson of the BCU is that large-scale catch-up efforts, while necessary in emergencies, are resource-intensive and cannot be the permanent solution. The global health community is now pivoting toward the Immunization Agenda 2030 (IA2030) and Gavi’s 2026–2030 strategy (Gavi 6.0).
These frameworks emphasize:
- Domestic Investment: Shifting the financial burden from international donors to sustainable, long-term national health budgets.
- Equity-Focused Outreach: Prioritizing the "hardest-to-reach" communities—those living in conflict zones or remote, underserved regions.
- Vaccine Confidence: Proactively addressing misinformation and rebuilding trust in medical institutions as a core component of health security.
World Immunization Week: A Call to Action
As the world observes World Immunization Week (April 24–30, 2026), the theme "For every generation, vaccines work" serves as a reminder of the mission. The Big Catch-Up has proven that with political will and coordinated global action, humanity can reverse even the most severe setbacks. However, the true test will be whether governments can maintain this momentum. As the UN agencies move forward, the message to the international community is clear: catching up is only the beginning. The real goal is to build a system that ensures no child, regardless of where they are born or the circumstances of their environment, is ever left behind again.
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