CDC addresses safety of thimerosal in vaccines against H1N1 flu

The Centers for Disease Control and Prevention posted this “fact sheet” about thimerosal in H1N1 vaccines on its Web site Jan. 4. The CDC has other information about H1N1 at

“The CDC is aware that pregnant women, parents of young children and others may have questions about the safety of thimerosal in vaccines against 2009 H1N1 flu. Here is some information to help you make decisions.

“Thimerosal is a mercury-containing preservative that is added to multidose vials (vials containing more than one dose) of vaccine to prevent contamination and growth of potentially harmful bacteria. This may occur when a syringe needle enters a vial as a vaccine is being prepared for administration. Such contamination could cause serious local reactions, illness or death.

“Thimerosal is a very effective preservative that has been used since the 1930s to prevent contamination in a number of products including some multidose vials of vaccines,” the CDC wrote.

“Data from 19 studies show no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor local injection site reactions like redness and swelling at the injection site.

Because “influenza vaccines are produced in large quantities for annual immunization campaigns,” the CDC explains, “some vaccines are produced in multidose vials.”

“FDA licensed (approved) both multidose vials and single-dose units of the 2009 H1N1 flu vaccine. The multi-dose vials of 2009 H1N1 flu vaccine contain thimerosal, while injectable single-dose units do not.

“In addition, the live-attenuated version of the vaccine, which is called LAIV and administered as a nasal spray, is produced in single-units and does not contain thimerosal.

“Some priority groups may not be able to find injectable thimerosal-free 2009 H1N1 flu vaccine due to a recent recall of pre-filled, single-dose syringes manufactured by Sanofi Pasteur. Since LAIV is only approved for people from 2 through 49 years of age who are not pregnant and do not have certain health conditions, this means pregnant women and children from ages 6 through 23 months may have difficulty obtaining a thimerosal-free 2009 H1N1 vaccine.

“It is important to keep in mind that severe illness and possible death can be associated with influenza, and vaccination is the best way to prevent influenza infection and its complications.”

The CDC said it “places a high priority on vaccine safety, surveillance and research” and “is aware that the presence of the preservative thimerosal in some vaccines and misconceptions of a relationship to autism has raised concerns.

“These concerns make the decisions surrounding vaccinations confusing and difficult for some people, especially some parents.

“Most research done in the United States, and around the world, shows no link between thimerosal in vaccines and autism, a neurodevelopment disorder,” the CDC concluded. “In fact, sadly, autism rates have actually gone up since thimerosal was taken out of childhood vaccines in 2001, providing further evidence that thimerosal-containing vaccines are not related to autism.”