Components other than antigen in vaccines include suspending fluids, such as sterile water, saline, culture media, adjuvants, stabilisers, preservatives and antibiotics to prevent bacterial contamination.
Thiomersal is a preservative that contains mercury and has been used as an additive in vaccines and biological substances for some 70 years because it prevents bacterial and fungal contamination, particularly in multidose containers. In 1999, the American Academy of Paediatrics and the US Public Health Service recommended, as part of the effort to reduce exposure to mercury, that the thiomersal content of vaccines should be reduced or replaced with formulations which do not contain thiomer-sal as a preservative as soon as possible, without unnecessary disruption of the vaccine system. It should be noted that the risk, if any, to infants from exposure to thiomersal is believed to be slight. The demonstrated risks for not vaccinating children far outweigh the theoretical risk for exposure to vaccines containing thiomersal during the first 6 months of life. Single and multiple antigen vaccine preparations, e.g. Hib and hepatitis B/ Hib vaccines, are available and others are in preparation.
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