Relevance of additives and adjuvants in vaccines for allergic and toxic side effects

Side effects of vaccinations can have different causes. Substances admixed to vaccines may produce allergic or toxic reactions. The significance and importance of causal associations is discussed in this paper. A table is added listing the most important substances in vaccines, such as inactivating substances, preservatives, stabilizers, adjuvants, and residual substances derived from production processes. Among possible allergic reactions type I reactions, as the most undesirable ones, should be avoided. In this respect, vaccines against yellow fever are the most important ones. With respect to antibiotics it should be stressed that penicillin and cephalosporines are not contained in any of the vaccines. The significance of side effects caused by ethylmercury as a preservative (thiomersal) is extendedly discussed in the literature. Allergy against this substance is common among the population, manifested as type IV reactions following superficial antigen administration. It has been shown that deep intramuscular injection of thiomersal-containing vaccines may be administered even to persons who are allergic to this substance without risk of side effects. Regarding toxic side effects after application of thiomersal, several studies have disproved a causal relation between thiomersal exposure and developmental disorders. Nevertheless, the general recommendation is to use thiomersal-free vaccines, unless no other preparations are available. In these cases risk of morbidity and mortality from the vaccine-preventable diseases outweigh by far any theoretical risk from ethylmercury.