Responses of elderly subjects to monovalent A/USSR/77 (H1N1) and Trivalent A/USSR/77 (H1N1)-A/TEXAS/77 (H3N2)-B/Hong Kong/72 vaccines.

Antibody responses to vaccination with monovalent A/USSR/77 (H1N1) and trivalent A/USSR/77 (H1N1)-A/Texas/77 (H3N2)-B/Hong Kong/72 vaccines were examined in a group of elderly persons most of whom had received more than 1 influenza vaccination in the previous 5 yr. Seventy-two per cent had a fourfold or greater increase in hemagglutination inhibition (HA1) titer to A/USSR and 92% had postvaccine titers equal to or greater than 1:40. There were no differences in antibody responses to A/USSR between recipients of monovalent and trivalent vaccines. No booster effect of a second injection of A/USSR was observed in subjects who had failed to respond to the first injection. Although there was a significant correlation between postvaccine HAI titers to A/USSR and to A/Texas, the responses to A/Texas and B/Hong Kong were modest or minimal compared with those to A/USSR. This serologic data may be relevant to the results of surveillance studies that suggest a limited advantage of repeated vaccinations with H3N2 subtypes and should help in evaluating the results of this practice.