An attenuated influenza virus vaccine: reactogenicity, transmissibility, immunogenicity and protective efficacy.

A more effective influenza virus vaccine must be capable of inducing a greater degree of protection against the disease while causing fewer unwanted side effects. If the vaccine is an attenuated one, it should not be transmissible unless it can incontrovertably be shown to be genetically stable and not mutate to a more virulent form. One approach for producing an attenuated strain has been to select for horse serum inhibitor resistance. Such a strain (ANN strain, Recherche et Industrie Thérapeutique) was tested for the above characteristics. The vaccine (containing 10-7 50 percent egg infectious doses) and placebo was administered in a double-blind fashion to 37 volunteers in 2 doses 2-3 weeks apart. Volunteers were housed so that a vaccinee and control shared a room for 4 days following immunization. The only side effects noted were mild rhinorrhea and sore throat in 3 vaccinees. There was no evidence of vaccine virus having been transmitted from a vaccinee to a control individual.A 4-fold or greater rise in serum antibody was noted in 13/19 vaccinees following either the 1st or 2nd dose. Only 1/18 controls showed such a rise. A similar nasal antibody rise was noted in 15/19 and 1/18 of the vaccine and placebo groups respectively. Following virulent challenge 7 of 18 in the control group, and 1 of 19 vaccinees, became ill.