Antigenic Similarity Between the First and Later Egg Passage Strains of Freshly Recovered Influenza A Viruses

Abstract
Cross-neutralization expts. in ovo with 1st and later chick embryo passage strains of freshly-recovered influenza A viruses showed no definite difference in their antigenic composition. However, the reactivity relative to guinea pig and chicken erythrocytes underwent a rapid and profound change between the 1st and 2d embryo passages.