Antigenic Variation of Asian Influenza Virus. ∗

Summary

Asian or “A” viruses isolated at the State University of Iowa in the recent epidemic were tested against selected paired human sera. All sera which had a 4-fold rise in titer by the complement fixation test also had a significant rise in titer by the hemagglutination inhibition test when several “A” viruses were used as antigens. Neither viruses nor sera were chemically treated. There was a distinct variation in antibody response to “A” viruses when tested by hemagglutination inhibition. Possible causes of this variation have been discussed.