Oral influenza vaccination with live attenuated viruses. 2. Protective efficacy during a type A(H3N2) epidemic

151 subjects, orally immunized with live attenuated influenza virus of the Institute for Viral Preparations of Moscow (bivalent A(H3N2) England 72 and B vaccine) and 66 non vaccinated cohabitants were studied during an epidemic caused by strains similar to A/Port Chalmers/73. 5 cases of disease were virologically or serologically ascertained among the vaccinated (morbidity 3.3%) and 8 among the non-immunized cohabitants (12.1%). The difference turned out statistically significant. By comparing the incidence of the disease in the two groups the protection resulting from vaccination was 72.6%.