Enhanced effect of repeated administration of bacterial vaccine against viral respiratory infection.

Administration of a standard bacterial vaccine (SBV) affords some protection against influenza infection in mice if given 4 to 5 h before inoculation of the virus. This effect was enhanced by repeated injections of SBV 7 and 14 days earlier, as measured by the length of survival, mortality rate, development of gross pneumonia, and virus multiplication in the lungs. Serum interferon levels were likewise enhanced by immunization with SBV, which may, at least in part, explain the increased preventive effect.