Failure of Inactivated Influenza Vaccine to Protect an Aged Population

Asian influenza developed in 36 of 176 residents of a county home for the aged four weeks after 80% of the residents had received the second of two doses of influenza virus vaccine. In addition, 60% of the residents had been inoculated with two doses the previous fall. Disease incidence had no discernible relationship to vaccination, and failure to protect apparently resulted from low postinoculation antibody levels. Antigenicity of another vaccine was studied in 35 laboratory employes; 21 had no antibody response, and only 6 had fourfold or greater titer increases. Since apparent lack of potency was manifested by vaccines from three different manufacturers, these results suggest that inadequate potency of commercially obtained inactivated influenza virus vaccine may be a greater problem than is generally realized.