Robert F. Kennedy Jr.’s decision to overhaul a key committee on vaccine policy has left the country’s vaccine infrastructure “critically weakened,” former members of the group said in a piece published in JAMA on Monday.

A senior scientist at the U.S. Centers for Disease Control and Prevention has resigned, warning that changes in leadership may weaken the country's vaccine program.

The medical community is bracing for attacks on, and the possible dismantling of, federal recommendations for safe, lifesaving childhood vaccinations after health secretary and fervent anti-vaccine advocate Robert F. Kennedy Jr. abruptly fired all 17 members of a federal vaccine advisory committee Monday.