A CDC advisory panel voted 5–1 to recommend only flu vaccines without the preservative thimerosal, a mercury-containing compound used as a preservative in vaccines and other drugs. Doctors and physician advocacy groups warn that the decision could fuel vaccine hesitancy.

Thimerosal is an ingredient that helps keep vaccines pathogen free. Health and Human Services Secretary Robert F. Kennedy Jr., a noted vaccine skeptic, has falsely stated the ingredient is a contributing factor in causing autism. In recent decades, the preservative largely has been phased out of vaccines, even as autism rates continue to climb.