Prevalence of hemagglutination inhibition antibody to current strains of the H3N2 and H1N1 subtypes of influenza A virus in sera collected from the elderly in 1976.

Sera were collected in 1976 from 182 individuals born between 1876-1935, who included patients in a large local nursing home in Orange County, California, and patients and staff at the University of California, Irvine Medical Center. Sera were treated with receptor-destroying enzyme and assayed for hemagglutination inhibition (HI) antibody to recent strains of influenza A virus. The antigens tested were: A/Victoria/3/76 and A/Texas/1/77 for subtype H3N2; A/New Jersey/8/76, A/X53 and A/Swine/1976 for the A/swine influenza virus-like strains of subtype H1N1; and A/Brazil/11/78, A/Fort Monmouth/1/47 and A/Francis Warren/1/50 for the A/Fort Monmouth/47 virus-like strains of subtype H1N1. For individuals grouped by five- and 10-year intervals of the year of birth, the geometric mean and standard error for HI antibody to each antigen were calculated and plotted vs. date of birth. The results indicate that for a majority of individuals born between 1876-1900, the level of HI antibody would be protective against H3N2 but not against the strains of H1N1. In addition, a majority of individuals born between 1900-1925 had levels of antibody that should be protective against both H3N2 and the A/swine influenza virus-like strains of H1N1 but not against the A/Fort Monmouth/47 virus-like strains of H1N1. These findings could be important when deciding on the antigenic composition of vaccines to be used in those age groups that are most vulnerable to the complications of influenza. In addition, data were obtained that suggest that the A/Fort Monmouth/47 virus-like strains of H1N1 recycle in 35-40 years rather than in 65-70 years as has been demonstrated previously for H2N2 and H3N2.