The Impact of COVID-19 on Immunization: What We Feared, and What We Now Know

While the global community confronted the COVID-19 pandemic head-on in 2020, working frantically to stem the spread of new infections and help health systems cope with an unprecedented crisis, children around the world began missing out on basic, life-saving vaccinations. Widespread stay-at-home orders and social distancing measures necessary to curb the spread of the coronavirus created several unintended consequences, among the most serious of which was the grounding or drastic scaling back of immunization and routine health services across most countries.

World Immunization Week, celebrated annually in the last week of April, was low-key that year and without its usual flurry of activities. It felt like a somber moment. It still does, in some ways, even now.

The foundation we built - and what was at risk

Since the introduction of the Expanded Programme on Immunization in 1974, the world has seen remarkable reductions in illness and death from vaccine-preventable diseases. Annually, vaccinations prevent an estimated 2 to 3 million deaths of children under five globally. Immunization has rightly been called one of the most cost-effective public health interventions ever developed.

Yet progress had already stalled before COVID-19 arrived. Global DTP3 (diphtheria-tetanus-pertussis, 3rd dose) coverage, a standard benchmark for immunization system performance, had plateaued at around 86 percent since 2010, leaving nearly 20 million under-immunized or completely unimmunized children every year. Of these, 13.5 million received no vaccinations at all. These were not abstract numbers. They represented real children, in real communities, already falling through the gaps of systems that were not reaching them.

COVID-19 did not create this vulnerability. It exposed and deepened it.

How the pandemic impacted immunization systems

The disruption was swift and severe. Travel restrictions and lockdowns led to mass vaccination campaign suspensions across dozens of countries. In conflict-affected and fragile settings, where vaccination campaigns had long served as a platform for delivering integrated child health interventions including vitamin A supplementation, malaria prevention, and nutrition support, the suspension meant the most vulnerable children lost access to multiple life-saving services at once.

Routine immunization services were similarly affected. Supply chains broke down. Vaccine stockouts became widespread. Parents and caregivers, themselves subject to lockdowns, faced travel barriers and genuine fears about crowded vaccination sites. Health workers, already stretched, were redeployed. Even where services remained technically available, demand collapsed.

The polio eradication effort, one of global public health's most important long-term projects, faced a particular threat. Campaign suspensions in Afghanistan and Pakistan, the last two countries with ongoing wild poliovirus transmission as of 2020, risked reversing hard-won gains. In other countries, which had successfully stopped wild poliovirus transmission, the risk of reversal of these gains was real and deeply concerning.

In a 2020 peer-reviewed paper published during the early weeks of the pandemic, my co-authors and I outlined a systematic approach to closing the immunization gap that COVID-19 was creating, arguing that restoring and protecting routine immunization required urgent, coordinated action across health systems, governments, and communities. The concerns we raised proved well-founded.

The warnings were clear. The question was whether the world would act on them in time.

What we now know: a reflection on COVID-19’s impact on immunization

Six years later, the data tells a sobering story - but not an entirely hopeless one.

Global immunization coverage did fall. According to analysis from the 2023 Global Burden of Disease data, of which I was a co-author, global DTP3 coverage was 4.2 percentage points lower in 2021 than it would have been in the absence of the pandemic, the steepest single-year decline. Between 2020 and 2023, an estimated 15.6 million fewer children received DTP3 globally than would have been vaccinated without COVID-19 disruptions. The global number of zero-dose children, those who received no routine vaccinations at all, rose to a pandemic peak of 18.6 million in 2021, up from 14.7 million in 2019. As of 2023, coverage had still not returned to pre-pandemic levels. The children most likely to be missed were, as predicted, those already left out of routine immunization services, in conflict zones, remote communities, and urban informal settlements.

Looking ahead, the study's reference scenario forecasts global DTP3 coverage reaching only 81.3% by 2030, well short of the Immunization Agenda 2030 target of 90%, achievable only under the most optimistic scenario. Sub-Saharan Africa faces the steepest climb, with more than half of the world's zero-dose children concentrated in just eight countries, five of them in Africa: Nigeria, Democratic Republic of the Congo, Ethiopia, Somalia, and Sudan.

Measles cases and outbreaks increased in multiple regions, exactly as the outlook from 2018 and 2019 data had predicted. In 2022 alone, 33 countries and territories reported substantial measles outbreaks. Disruptions to polio vaccination campaigns contributed to setbacks in eradication efforts, with new outbreaks of wild polio virus occurring in countries that had been polio-free. The consequences of missed vaccinations are not theoretical; they are counted in outbreaks, hospitalizations, and preventable deaths.

The resurgence of vaccine-preventable diseases is worth discussing. Measles was eliminated in the United States in 2000. However, according to the JHU IVAC Measles Tracker, in 2025, the United States recorded more than 1,200 confirmed measles cases across 38 states, with over 160 hospitalizations. Nearly all cases occurred in unvaccinated individuals or those with unknown vaccination status. There were also three measles-related deaths in the United States in 2025. Likewise, according to WHO data, in 2024, Europe recorded its highest number of measles cases in more than 25 years.

These outbreaks are not isolated incidents; they are the consequence of years of eroding vaccine confidence, COVID-19-related disruptions, and the failure to close coverage and vaccine equity gaps before the pandemic. The World Health Organization identified vaccine hesitancy (the reluctance or refusal to vaccinate despite the availability of safe and effective vaccines) as one of the ten leading threats to global health, pre-pandemic. COVID-19 significantly amplified this threat. In many communities, declining trust in public health institutions and the spread of misinformation exacerbated doubt about childhood vaccines as well. The consequences are now counted in outbreaks, hospitalizations, and deaths that were entirely preventable.

Addressing vaccine hesitancy requires more than information campaigns. We must rebuild trust in public health services through community engagement, culturally responsive health communication, and the consistent leadership of trusted health workers who are known and trusted in their communities. This will require listening before talking and acknowledging that for some communities, historical experiences of medical mistreatment make vaccine skepticism not irrational but deeply rational and understandable. Rebuilding trust in our public health and preventive services requires accountability, honesty, humility, and sustained relationship.

The recovery of vaccination coverage has been uneven. Some countries implemented effective catch-up vaccination campaigns, including through WHO's Big Catch-Up initiative, once restrictions were lifted. Others are still working to close the gaps. Without sustained investment and intensified effort, coverage targets for 2030 remain at risk in several high-burden countries.

What this period also revealed, perhaps most clearly, is the fragility of immunization systems that were already under-resourced before the pandemic. COVID-19 was the stress test that many health systems failed, not because their health workers lacked commitment or skill, but because the systems themselves lacked the resilience, the financing, and the community-level infrastructure to sustain essential services under pressure.

Where do we go from here?

The lessons of 2020 are clear even if the political will to act on them remains uneven.

Health systems must be built for resilience, not just efficiency. Catch-up vaccination must be treated as an ongoing priority, not a post-crisis fix. Supply chains must be diversified and strengthened at the last-mile. Community health workers, the backbone of outreach immunization in low-resource settings, must be supported and compensated. And immunization programs must be integrated with broader primary health care systems so that a disruption to one service does not cascade into the collapse of all services.

Innovative delivery strategies matter too. Mobile clinics, school-based vaccination, community-led outreach, digital immunization registries are not optional additions. For the children most likely to be missed by fixed-site services, they are the difference between tailored protection and preventable death.

Most importantly, the global community must recommit to the principle that drove the creation of the Essential Programme on Immunization more than fifty years ago: that every child, everywhere, has the right to protection from vaccine-preventable disease. That right does not pause during a pandemic. It does not apply only to children in high-income countries. And it cannot be contingent on geopolitical stability, supply chain reliability, or the absence of the next global crisis – because the next one is always lurking.

The global community must deliver on the right of every child everywhere to health care and lifesaving vaccinations, even in the face of a global pandemic. We cannot afford to fail the world's children in this mission.

We knew what was at stake in 2020. We now know what it cost. The remaining question is whether we will build systems strong enough to protect the next generation of children when the world is tested again.