Pennsylvania officials this week reported that two unvaccinated residents died after being infected with measles, with Gov. Josh Shapiro stressing that vaccinations could have averted the deaths.

But the announcement quickly came under fire, as a clash erupted between Shapiro, a vaccine-promoting Democrat, and U.S. Health Secretary Robert F. Kennedy Jr., a Trump administration appointee with a history of raising alarms about established vaccines. Kennedy said in a social post the deaths "may even have been altogether fabricated."

Kennedy's attack echoed statements he made last year, when three measles-related deaths were recorded. Kennedy questioned whether one of the children who died was killed by measles.