Once considered eliminated in the United States, measles has made an unwelcome return.  

Cases dropped during the COVID-19 lockdown but have since risen, a troubling surge of 277 cases in 2024 through November 7 relative to just 59 cases in 2023. Nearly half of those infections were in children under 5. More than 9 in 10 U.S. measles cases in the past four years stemmed from international travel, a stark reminder that illness knows no borders in a globalized world. In the first quarter of 2024 alone, 16 million Americans voyaged abroad but, too often, unvaccinated American children who haven't traveled end up sick.  

In the United States, family lore often recalls measles as a mild, mid-twentieth century illness, a temporary inconvenience marked by a red, spotted rash that kept children home from school. Less remembered, however, is that about 1 in 3 measles cases leads to complications—including pneumonia, brain inflammation, or blindness. A universally pernicious virus, it is far more infectious than COVID-19, leaving anyone without full vaccination vulnerable to infection. These attributes can yield frequent outbreaks, hospitalization, and death. 

For years, the United States maintained high vaccination rates, immunizing more than 95% of kindergartners. But when the COVID-19 pandemic hit, vaccination rates plummeted, leaving a quarter of 1 million children un- or undervaccinated as they enter school each year. As a result, the United States now faces a growing vulnerability to a virus once thought beaten.  

The trend is equally alarming in other parts of the world. Since 2020, outbreaks of vaccine-preventable diseases have been rising steadily, fueled by the breakdown of immunization efforts caused by the strain of the COVID-19 pandemic. In 2023, 74% of children worldwide received the recommended two doses of the measles vaccine but almost 14.5 million received no routine vaccines at all.  

The global resurgence of measles is an escalating threat to public health everywhere. Earlier this year, more than 1,200 children under 5 died from measles and malnutrition in Sudanese refugee camps within four months after being displaced from their homes. A similar pattern is emerging in other war-torn countries, including Democratic Republic of Congo, Ethiopia, Iraq, and Mozambique, where nascent measles outbreaks are taking root. As long as war and instability persist, so will this deadly disease.   

War kills in many ways, but one of its more enduring tolls is the resulting humanitarian crises—including the destruction of health systems. In Bangladesh, outbreaks of long-gone infections such as diphtheria have occurred in areas with high refugee populations. The polio outbreak in Gaza was a wake-up call, prompting the United Nations to negotiate a brief ceasefire to ramp up vaccination efforts. Those examples underscore a grim reality: the longer conflict endures, the more vulnerable the world's children become to preventable diseases, including measles, once relegated to history. 

Vaccine misinformation is a major factor behind measles outbreaks in the United States as well as overseas. Spillover hesitancy—when concerns about one vaccine, such as that for COVID-19, are applied to multiple vaccines—may be behind increased vaccine exemptions. Misinformation in the United States has led to dramatic drops in vaccine uptake in a range of international settings. In Brazil, declining childhood immunization rates occurred after politicians seeded online disinformation. Brazil has since made significant strides in debunking vaccine rumors.  

U.S. donors stepped forward when COVID-19 hit, but the mobilization of resources for the pandemic cut into the aid for other primary health-care initiatives, such as Medicaid, in the name of balanced budgets. Overseas development aid from the largest international donors that focused on all other global health services, including measles surveillance programs, has declined since its peak in 2017. 

Although 2022 saw a modest recovery, a renewed approach to global health financing is imperative to safeguarding the advancements achieved and enhancing preparedness for future health emergencies. In particular, global measles elimination efforts should be strengthened through an infusion of funding from a broad multilateral coalition. 

As the United States strives to bolster efforts protecting children, it should not neglect those abroad. The country's humanity—and its health—are inextricably linked to the lives of people devastated by conflict. The U.S. administration's recent $1.58 billion pledge to Gavi, the Vaccine Alliance, is an encouraging step toward vaccinating the world's hardest-to-reach children over the next five years. 

This vision is not just about protecting children living far away; it's about safeguarding future generations here at home. In an interconnected world, no one is safe until everyone is. 

AUTHOR'S NOTE: The authors' views are their own and not those of the Johns Hopkins University.