Twenty-nine boys in a boarding school were present during a large outbreak of influenza A H1N1 in 1978 when 27 were infected, 21 with clinical influenza. These boys were bled annually and were still in school when another outbreak of influenza A H1N1 occurred in 1983. Twentythree of them were reinfected but only nine had symptoms. These results are compared with the experience of a similar group of boys in the early years of the influenza A H3N2 era.

Four antigenic variants of the neuraminidase (NA) of A/Texas/77 (H3N2) virus were selected using monoclonal antibody at a frequency of one variant in 105 parental virions. The antigenic variants failed to react serologically with the monoclonal antibody used for their selection in vitro. The antigenic variants failed also to react serologically with a proportion of sera from children and adults although all of the sera reacted with the parental A/Texas/77 virus. Thus, certain human sera have a restricted antibody repertoire to influenza NA antigen which might enable virus antigenic variants to avoid anti-NA antibody-mediated neutralization in nature.

A small epidemic of nursery-associated hepatitis A (HA), in which silently infected children played a cryptic role in transmitting the illness to adult contacts, was investigated. It was found that a male nurse had transmitted HA to four children before he fell ill. He was not heard from for about two months as he was a part-time worker and was admitted to a local hospital in another prefecture. Two of the four silently infected children transmitted HA to their parents who then revealed the presence of nursery-associated HA. The epidemic was terminated by injection of human gamma globulin to nursery children and to antibody-negative parents, nursery staff and other contacts except for two breakthrough cases.