What is thimerosal, does it have side effects and why is RFK Jr. removing the controversial preservative from the flu shot? Here's what to know.

Flu shots that have more than one dose of vaccine contain thimerosal; other versions don’t have it. HHS said Wednesday that vaccine makers have said they have the capacity to replace the shots that do contain thimerosal so that vaccine supplies aren’t interrupted.

The decision follows last month’s vote of the CDC’s revamped vaccine advisory committee. Thimerosal, mostly removed from vaccines decades ago, has long been a target of anti-vaccine advocates for unfounded links to autism and adverse health outcomes.