Studies on Influenza (particularly Influenza A/Asia/57) among Infantile Grips

III Isolation of virus, serum neutralization antibody titer and reinfection

Abstract

Isolation of virus, determination of neutralization antibody titer and reinfection were investigated on the infants serologically diagnosed as influenza A/Asia/57. The results were as follows;
1. Virus isolation was carried out n 13 cases by means of intraamniotic inoculation of hen egg. The virus isolated from gurgle water of 2 cases on the econd day of illness was identified as influenza A/Asia/57. These 2 strains possessed a good HI-antibody-producing ability and reacted well with the antiserum.
2. The serum neutralization antibody titer (NT Value) was determined with paired samples of 8 cases after the incubated hen egg method. All the cases demonstrated a significant rise. he rise of NT value paralleled with that of HI value. Whereas the fall of HI occured earlier and more rapidly, the NT value did not decline in 3 months not only in all the cases, but was higher in one case in the 400 th day of illness than in the acute stage.
3. Four cases might be considered as reinfection out of 86 cases observed since eptember 1957 (4.7%). The reinfection was not considered to play an important role epidemiologically in an epidemic of several months.