The Americas — North, Central, and South — is the only region of the world that has ever managed to stop endemic transmission of measles. But that hard-won victory against the highly contagious virus is on the verge of being rolled back.

This week an expert committee of the Pan American Health Organization (PAHO) is meeting in Mexico City to study measles transmission data from the region. Canada’s massive — by contemporary standards — and long-running measles outbreak is almost certain to trigger a finding that the country’s, and thus the entire region’s, status as having eliminated measles has been lost.

Though largely symbolic, losing measles elimination status will smart for the country, which had stopped ongoing measles transmission for more than a quarter century. Canada was declar

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