Public health authorities reported on Feb. 21 that an ongoing measles outbreak in Gaines County, Texas and Lea County, New Mexico was already the largest in decades. Of the 90 cases in Gaines County, 26 involved toddlers under four years of age; 51 children between five and 17 were afflicted, and 16 people had been hospitalized. All but five of the infected individuals had not been or were not known to have been vaccinated.

Last week, the number of cases grew to 124 and one child, who was unvaccinated, died — the first U.S. measles fatality in a decade.

Vaccination of children is required in all 50 states. In 2013, 7.5 percent of parents or guardians in Gaines County filed for an exemption, while a decade later, 17.5 percent did so — one of the highest exemption rates in the country.

Exemptions have increased dramatically nationwide. As of the 2023-24 school year, about 280,000 kindergartners had not taken shots for measles, mumps and rubella. Fourteen states report exemption rates exceeding 5 percent, enough to prevent the acquisition of “herd immunity.”

It should now be clear that the widespread dissemination of groundless conspiracy theories is undercutting confidence in the safety and efficacy of vaccinations and presenting a clear and present danger to the health of all Americans.

In the early 20th century, measles — one of the most contagious of all diseases — killed about 6,000 Americans each year. By........

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