Robert F. Kennedy Jr. has repeated that not enough childhood vaccines have been tested in clinical trials against a placebo.

At the first meeting of a controversial new group of vaccine advisers to the US Centers for Disease Control and Prevention, the committee announced new plans to study established vaccine guidelines.

The newly formed vaccine advisory committee handpicked by Health and Human Services Secretary Robert F. Kennedy Jr. announced that it would examine the cumulative effect of the childhood vaccine schedule and reevaluate hepatitis B immunization recommendations — moves that could shift long-standing practices of how and when children are immunized in the United States.