All 17 experts from the Advisory Committee for Immunization Practices who were replaced last month by Robert F. Kennedy Jr. called the health secretary's new picks "inexperienced and biased."

Dr. Noel Brewer, a former ACIP member removed by Kennedy and a professor in the department of health behavior at the University of North Carolina Gillings School of Global Public Health, told ABC News that since the upheaval of the ACIP, vaccination has changed in the U.S. in a "fundamental" way and that the committee has "lost credibility."

Though a strong promoter of vaccinations, Cassidy persuaded wary fellow Republicans to confirm Kennedy, President Donald Trump’s nominee to run the U.S. Department of Health & Human Services.