Studies on the Epidemic of Influenza Type B

especially from a standpoint of serologic epidemioogy

Abstract

Influenza type B Amakusa strain which gave rise to epidemic from October of 1963 to February of 1964, was a virus having a wide range of antigenic structure.
The rise of serum antibody titers after epidemic was observed against all strains of type B studied. The subsequent reduction of hemagglutination inhibition antibody titers, however, supported the ‘doctrine of the original antigenic sin’, the initial infection of type B Setagaya strain among school children being assumed.
A latent infection of 40 percent was concluded from the antibody distribution on complement fixation before and after epidemic.
The antibody titer level using a single serum for judging an experienced infection was decided from the results of antibody distribution before and after epidemic and from the results of antibody estimation on pair sera from the patients. The titer was 20 on the complement fixing antibody and 128 on the hemagglutination inhibition test with Amakusa and Setagaya strain simultaneously. It was pointed out using this lvel that already from 1960 there were some cases assumed the infection due to the virus strain of the present epidemic.
Antibody titers of the school children in October 1964 were considerably high while those of infants and adults were relatively low. It is therefore presumed that the influenza epidemic might occur to some extent among infants and adults, but in contrast it will not occur among school children unless new variant strains appear.