Canada Poised to Lose Measles Elimination Status as Outbreak Passes One Year; U.S. May Follow

This week, Canada crossed a line that public health officials have been watching for months. A measles outbreak that began in October 2024 in New Brunswick, on the country's eastern seaboard, has now run for a full year without a break. As of Tuesday, more than 5,000 cases had been reported, and two babies have died.

The length of that run matters more than almost anything else. Daniel Salas, an immunization expert with the Pan American Health Organization, put the standard plainly: a country loses its elimination status after 12 months of continuous transmission of the same genotype and strain of the virus. Falling vaccination rates in both Canada and the United States are among the other criteria, but sustained spread is the most significant one. Canada reached that mark this week.

PAHO is part of the World Health Organization, and it is the body responsible for deciding whether countries in North, South and Central America have eliminated measles. It is set to meet next week in Mexico City to analyze measles data through the end of October. A PAHO spokesman said that when a country loses its status, a corrective action plan is requested to guide its efforts to regain elimination.

The history behind the label is short. Canada eliminated measles in 1998, and the United States followed in 2000. Salas called that "a huge achievement," and noted that when the region sustains elimination, it is also acknowledging each country's work to get there.

The American picture is different in timing, though not necessarily in direction. The CDC has logged at least 1,618 measles cases in the U.S. so far this year. The outbreak that threatens the country's status began in West Texas in late January. More than 800 people in Texas and New Mexico have been infected, and the outbreak has spread to other states. Three people have died, two of them young girls.

Because that outbreak started in January, Salas said it is highly unlikely the U.S. will lose its status at next week's meeting; the 12-month clock simply has not run out. A further question remains open, too. Spread in Arizona, Utah and South Carolina is ongoing, and it will take time to analyze whether those cases are linked to the West Texas outbreak. If they are, they extend one chain of transmission. If not, the picture changes.

In Canada, the response from clinicians has been blunt. Dr. Isaac Bogoch, an infectious diseases expert at the University of Toronto, told CTV Television Network in Toronto this week that the likely loss of status is "a wake-up call that we need to do better in vaccinating our general public so we don't have outbreaks like this."

What to watch is the Mexico City meeting next week, where PAHO reviews the data through October, and then the slower work of tracing whether the Southwestern and South Carolina cases belong to the Texas outbreak. That analysis will help determine when the U.S. faces the same decision Canada is facing now.