Reactions and serologic responses in young children and infants after administration of inactivated monovalent influenza A vaccine.

Infants, two years of age and under, received zonally purified whole-virus A/Aichi/2/68 (H3N2) influenza vaccine. Febrile responses, including one febrile convulsion, were observed in nine of 13 (69%). There was a fourfold rise in serum-neutralizing antibody in nine of 11 (82%) of those lacking initial antibody titers. Purity of the vaccine was documented by electron microscopy, absence of egg protein, and very low levels of endotoxin (0.048mug/dose). It is concluded that the toxicity of vaccine is related to the virus itself and that, despite the good antibody response, influenza vaccine should be administered only to children two years and under at high-risk of complications from influenza, if at all.