Homologous and heterologous antibody responses to subunit influenza virus vaccine

In a group of 32 adult volunteers given subunit influenza virus vaccine containing 250 international units (i.u.) of A/Victoria/3/75, 250 i.u. of A/Scotland/840/74 and 300 i.u. of B/Hong Kong/8/73, there were substantial increases in the geometric mean homologous haemagglutination-inhibiting (HI) antibody titres. There was also substantial boosting of the antibodies to the earlier variants of the Hong Kong (H3N2) series and to a later variant of the Asian (H2N2) series. There was no boosting of antibodies to the A/FM/1/47 strain, a representative member of the H1N1 series, but two individuals showed substantial rises to A/PR/8/34 (HON1). There were increases in the HI titre of antibodies cross reactive with two recent isolations, A/Texas/1/77, and A/Victoria/35/77, but the majority of vaccinees failed to reach antibody titres likely to be protective against such strains.