Why measles outbreak in Pennsylvania poses risks beyond US borders

Decades after it was officially declared eliminated in the United States, measles has made a resurgence, with the US Centers for Disease Control and Prevention (CDC) announcing the third death of the year from the virus.

Matt Ferrari, director of Pennsylvania State University’s Center for Infectious Disease Dynamics, said the US was so successful at wiping out measles that it had “the luxury to forget” it was a serious problem.

“It’s been a long time, and for many of us in the United States, and in fact, throughout the Western Hemisphere, we have been able to forget how nasty measles is,” Ferrari told Al Jazeera.

Pennsylvania has been hit especially hard in the most recent outbreak. In September, the state sought emergency support from the CDC to control the spread, even as state and federal health officials quarrelled over the measles-associated death tally — differing over how deaths should be classified. State officials have recorded more than 1,200 cases and over 240 hospitalisations in 42 counties so far this year.

This spike in cases has raised concerns in neighbouring US states. On October 5, New York Governor Kathy Hochul declared a state disaster emergency in response to rising cases in rural areas, expanding the number of health professionals authorised to vaccinate and test people for measles.

“No one should get seriously ill or die from a vaccine-preventable disease,” Hochul said.

But experts warn that the risks extend far beyond US state borders. The US resurgence comes as measles cases increase globally, particularly in communities that are vaccine-sceptical or where there are gaps in healthcare access.

Vaccination coverage among US kindergartners has decreased from 95.2 percent during the 2019-2020 school year to 92.4 percent in the 2025-2026 school year. Experts warn that declining vaccination rates in one geographic location can leave people thousands of miles away vulnerable, making measles prevention a shared global responsibility.

Building trust in vaccine-sceptical communities

Pennsylvania reported in August that two unvaccinated people died of measles in Lancaster County, which is located in the South Central part of the state. Lancaster is considered the centre of Pennsylvania Dutch Country and home to the nation’s oldest Amish and Mennonite communities, both of which have under-vaccinated populations.

In Pennsylvania, public health officials have worked with community leaders to share information and expand access to vaccination. Joshua Good, principal of Ephrata Mennonite School in Lancaster County, where two students contracted measles earlier this year, worked with state officials to organise a pop-up vaccination clinic at the school.

He said officials also provided communication materials that the school adapted for its community and helped identify at-risk families.

While Good said the response was productive, he told state officials that the Mennonite community still holds a lot of vaccine scepticism.

“I said, look, if we do this, keep in mind, our community by and large…made that decision not because they don’t have access to the vaccines. They made the decision based on their own best judgement,” he told Al Jazeera.

Good, who is vaccinated and vaccinated his children, sees himself as an advocate within the community. If families have questions about measles shots, he will answer them as best he can.

“I have honest conversations with people, try to engage in respectful, charitable ways,” he said. “I’ll try to understand what their hesitancies are. That said, I respect their concerns.”

Although multiple community members received the measles vaccine at the Ephrata clinic, vaccination rates remain below the threshold for herd immunity.

Public health officials advocate for investing in robust community outreach before outbreaks happen.

“You can’t just show up in a community in an emergency– an emergency in which they might feel like you’re there to kind of blame them or shame them,” Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health, told Al Jazeera. “You need to know them so that they see public health as a resource rather than law enforcement.”

She said low vaccination coverage and distrust of the government allow measles to spread even when vaccines are available. But that shouldn’t stop governments from building rapport with vaccine-sceptical communities.

“I worry that by framing it around their demographics, it lets governments off the hook in terms of what they’re supposed to be doing, which is stopping the spread of this dangerous disease,” Nuzzo said.

Experts explain that declining vaccination rates put not only these communities but also immunocompromised people at greater risk for disease. Herd immunity in the wider population formerly helped shield those most vulnerable to infection.

“Those are communities that have been at risk for years,” Ferrari said. “But higher rates of vaccination in the communities surrounding them offered a barrier.”

The continental Americas was the first World Health Organization (WHO) region to eliminate endemic measles transmission in 2016. Maintaining that status requires high and consistent vaccination coverage. The Pan American Health Organization (PAHO) says coverage across the region remains below the target for both doses of the measles vaccine, contributing to noticeable consequences.

PAHO holds an annual RVC Measles Elimination Status Conference where an independent technical body of international experts monitors and reviews whether countries in the Americas have successfully eliminated measles, rubella, and congenital rubella syndrome. A country can lose its “elimination status” when the same measles virus genotype has circulated continuously for at least 12 months.

Last year, Canada became the first country in the continental Americas to lose its status after an outbreak that began in 2024. Some have warned that the US may be on track to lose its status this year.

But Dr Daniel Salas, executive manager of the Special Program for Comprehensive Immunisation at PAHO, told Al Jazeera that it’s not just the US that will be under review.

“We have Mexico, we have Bolivia that is going to be closely assessed because they could potentially lose status as well,” he said.

US Health and Human Services Secretary Robert F Kennedy Jr has repeatedly defended the US response to measles.

“We’re doing a better job than any country in the world at controlling the measles outbreak,” Kennedy said at an August 26 event in Florida. He cited higher case numbers in Mexico, Canada and Britain.

But Nuzzo said the repeated outbreaks across the US point to a country struggling to contain transmission.

“We have not seen it this bad,” she said. “It’s like this perpetual game of Whac-A-Mole. As long as there are vulnerable communities, as long as we don’t have strategies for early detection and rapid response and containment, measles will just keep on happening over and over and over again.”

Dr Salas told Al Jazeera that action within the first three days after a suspected case is critical, and health authorities should begin investigating and taking response measures without waiting for laboratory confirmation. Delays of a week or more can allow the highly contagious virus, marked by fever, coughing, and a whole-body rash, to spread further.

Experts warn that outbreaks cannot be treated as isolated local events. Scientific journals have found evidence that the virus strain in Canada’s latest measles outbreak was genetically linked to cases reported in US Mennonite communities. This was the same outbreak that resulted in Canada losing its measles elimination status.

“The spread of measles in the United States imperils other countries,” said Nuzzo. “It’s easy to kind of point to other countries and say that they’re the problem, but the reality is we’re all dependent on each other, and it’s very hard to protect ourselves when measles is spreading elsewhere.”