The mercury-based ingredient has prompted concerns from some organizations, although the CDC has said there is no evidence it causes harm.

A nonprofit anti-vaccine group founded by Robert F. Kennedy Jr. is suing him, in his capacity as secretary of the US Department of Health and Human Services, for failing to establish a task force to promote the development of safer childhood vaccines.

The CDC says there is no evidence of harm from mercury-based thimerosal.

Federal guidelines no longer recommend flu vaccines containing a preservative, used in a small percentage of vaccines, that has been falsely linked to autism.

The health secretary has made many inaccurate statements about vaccines. But the science is clear that vaccines have dramatically reduced childhood illness, disability and death.

Health Secretary Robert F. Kennedy Jr. recently announced a change to the Centers for Disease Control and Prevention's vaccine schedule that he says reflects a new approach to public health and personal choice.