Sherry Andrews, right, holds 13-month-old Jaqi Herrera’s hand after administering the first MMR vaccine dose to Herrera at the City of Lubbock Health Department in Lubbock, Texas, on February 27. Annie Rice/Reuters

The combination measles, mumps and rubella vaccine — better known as the MMR shot —should be split into three separate vaccines, US Centers for Disease Control and Prevention Acting Director Jim O’Neill said this week. His post on X included similar language posted on X by President Donald Trump in late September.

This proposal has raised alarms for many public health experts , who worry that splitting up the shots has no clear scientific justification but would increase the number of health care visits required to get vaccinated for measles, mumps and rubella; reduce

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