A preservative-free flu shot is a type of flu vaccine that does not contain the antimicrobial agent known as thimerosal. Thimerosal, a mercury-based compound, is an ingredient that's used in some ...

Medically reviewed by Lindsay Cook, PharmD The flu shot is the best protection against seasonal flu. This is why millions of people get the influenza vaccine each year. According to the World Health ...

thimerosal, in flu vaccines and other shots given to children and pregnant women. The move was made in response to fears that thimerosal might cause neurological conditions such as autism.