The administration to human beings of formalin-killed influenza virus, concentrated from allantoic fluid, resulted in a high order of antibody response within 2 weeks after injection. Even after 1 year the great majority of individuals vaccinated had antibody levels considerably above their prevaccination titer for the PR8, Lee, and a current 1943 strain. An investigation of the occurrence of epidemic influenza A in seven widely separated populations, 1 year after vaccination of part of these groups, showed that the attack rate among vaccinated persons was consistently lower than that of control individuals. The average reduction in attack rate was of the order of 35 per cent.

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