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... "We're living in a post-herd-immunity world. I think the measles outbreak proves that," said Dr Paul Offit, an expert on infectious disease and immunology and director of the Vaccine Education Center at Children's Hospital of Philadelphia.

"Measles -- because it is the most contagious of the vaccine-preventable diseases, the most contagious human disease really -- it is the first to come back."

The US eliminated measles in 2000. Elimination status would be lost if the US had 12 months of sustained transmission of the virus. As of 1 May, the US Centers for Disease Control and Prevention (CDC) reported 935 confirmed measles cases across 30 jurisdictions. Nearly one in three children under five years old involved in the outbreak, or 285 young children, have been hospitalized.

Three large outbreaks in Canada, Mexico and the US now account for the overwhelming majority of roughly 2,300 measles cases across the World Health Organization's six-country Americas region, according to the health authority's update this week. Risk of measles is considered high in the Americas, and has grown 11-fold compared with 2024. ...