H1N1 influenza and old people

A split-product influenza A vaccine which contained an influenza B strain (B/Hong Kong/8/73) and two influenza A strains, antigenically identical with A/Fort Dix/741/76 (Hsw1N1) and A/Victoria/3/75 (H3N2), was offered to personnel of the CPHL. Changes in the antibody status were followed with serum samples collected from 153 participants on the day of vaccination and 1, 13 and 18 months thereafter. During the two epidemic seasons in the trial period there were only four serological influenza A infections (2.6%) among the vaccinees. This is one eighth of the corresponding infection rate (22%) in the general population estimated on the basis of other indices. The vaccinees' antibody response was strongly influenced by the age of the individual subjects. During the trial period the decrease in the antibody titres slowed down. The geometric mean titres of homologous HI antibodies were still substantially higher at the end of the period than at the beginning. This also applied to heterologous antibodies against H1N1 viruses in persons born between 1926 and 1952. In participants born after 1952, the vaccine was not able to evoke these antibodies, and in participants born in or before 1925 the boosting effect was poor.

Protection by a polyvalent influenza vaccine and persistence of homologous and heterologous HI antibodies during a period of two epidemic seasons

Pyhälä¹

1980

Antibody status to influenza A/Singapore/1/57(H2N2) in Finland during a period of outbreaks caused by H3N2 and H1N1 subtype viruses

Pyhälä

1985

The incidence of haemagglutination inhibition (HI) antibody (titre greater than or equal to 12) to influenza A/Singapore/1/57(H2N2) in sera collected from a Finnish population in the summer of 1981 was 58%. Subjects born after 1968 were essentially seronegative, and a comparable low HI antibody status was also recorded among the elderly, the lowest being in people born during the period 1901-10. A small increase in antibody titre to the H2N2 virus was observed in the different age groups after infections with the H3N2, but not the H1N1, subtype influenza A viruses. The heterotypic response, which could be due to HI or NA antibodies, was restricted almost exclusively to subjects already exhibiting this antibody in acute phase sera. Moreover, the anamnestic boosting was not as strong as that described in earlier studies from samples collected at the beginning of the present era of H3N2 viruses. At population level, the HI antibody status to H2N2 was about the same at the beginning and end of the follow-up period which covered eight epidemic seasons. The results are discussed with respect to the doctrine of 'original antigenic sin' and to the threat of re-emergence of the H2N2 viruses.

Seroepidemiology of H1N1 influenza: the infection and re-infection rate in winter 1978–79

Pyhälä

Aho

1981

SUMMARYIt was observed that small children and pregnant women were affected to only a small extent by the HINI influenza outbreak of winter 1978-79. This supports earlier findings from the epidemic season of 1977-78 and demonstrates that the evolutionary changes in the epidemic virus were not reflected in any appreciable way in this curious phenomenon. The frequency of elderly subjects possessing antibodies against the epidemic HINX virus was low, and virtually equal in the pre-epidemic and post-epidemic sampling. This low attack rate contrasts with observations on young military servicemen, in whom the re-infection rate was high, thus indicating that the infection with the winter 1977-78 virus had conferred only modest protection against the closely related virus which caused the winter 1978-79 outbreak.