Why the US, Mexico and Guatemala may lose their measles-free status

The Pan American Health Organization's (PAHO) Regional Monitoring and Re-Verification Commission (RVC) began its annual conference on Tuesday to assess whether the United States, Mexico and Guatemala have maintained their measles elimination status. The commission, an independent panel of international experts in epidemiology, public health and virology, will review reports submitted by all 35 PAHO member states, with particular attention to countries experiencing prolonged outbreaks.

The review comes as a sharp resurgence of the virus has spread across the Americas, with the US experiencing its largest and deadliest measles outbreak in nearly 30 years. The US has held its elimination status since 2000, but it risks losing it this year. Mexico has also reported prolonged transmission, while Canada lost its status last November.

PAHO reported 57,666 confirmed measles cases across 17 countries and territories in the Americas between January and October 2026. The Americas became the first region in the world to eliminate endemic measles transmission in 2016, following decades of vaccination campaigns.

Status Determination Process

Experts at the conference evaluate whether infections result from separate introductions of the virus or whether the same strain has circulated locally. Under PAHO's criteria, a country loses its elimination status if the same measles virus strain continues to spread uninterrupted for at least 12 months in a country or defined geographical area.

Investigators use genetic sequencing to determine whether infections are linked to the same virus strain. They also examine epidemiological data to establish how the virus has spread and whether transmission has been interrupted. The commission considers vaccination coverage, healthcare systems' monitoring capabilities, and the speed of outbreak responses in its decisions.

Potential Consequences

Experts agree that the US will likely lose its measles elimination status, marking a reversal of a major public-health achievement. "It would be a disappointment, not a shock," Matt Ferrari told Al Jazeera. "This is moving backwards from a great public health achievement, and to see that backslide is just heart-wrenching."

Although the loss of status would not trigger any immediate consequences, those working in the field say it would be an embarrassment. The long-term effects include greater pressure on public-health systems, which must devote resources to identifying infections, tracing contacts, conducting laboratory tests, isolating patients and organizing vaccination campaigns.

When asked about how a country generally responds to losing measles elimination status, Asturias pointed to Brazil, which regained its measles-free designation in 2024 after launching a strategic vaccination campaign. However, he does not believe the US will mount a similarly robust response.

On Tuesday, Erica Schwartz, director of the US Centers for Disease Control and Prevention, said losing elimination status would not change the agency's approach to measles. "We're going to be doing the same exact thing that we've been doing today, which is working with the states," she told Reuters.

Ferrari said the announcement could nonetheless galvanize action at state and local levels by giving public-health officials and advocates shared language. "Think globally, act locally," he said. "We all will have the same language to talk about what's going on. And that's surprisingly important."

Next Steps

The commission's deliberations in Washington run until Friday. It will assess the evidence and make recommendations on the status of individual countries to PAHO Director Jarbas Barbosa, who will make the final determination. The official announcement is expected early next week following the conclusion of the conference.