Some have been revised to reflect new recommendations and some out of date questions have been removed. For this reason, you should not use older sets of these questions and answers. If you have additional questions about immunization or hepatitis B that would interest our readers, please send them to us.
Thimerosal is an effective preservative that contains ethyl mercury.
It has been used in small amounts to reduce the chance of bacterial growth in vaccines and other products since the 1930s. Most of these reports concerned allergic reactions. Although thimerosal contains ethyl mercury, there is no evidence that mercury received through vaccines is harmful to a child. For routine childhood vaccines there is at least one brand of each vaccine that does not contain thimerosal. It is critical that children continue to be vaccinated on time, even if a thimerosal-free vaccine is not immediately available.