Efficacy of subunit trivalent influenza vaccine in previously vaccinated children suffering from hemophilia

Abstract

OBJECTIVE: To assess humoral immune response to subunit trivalent influenza vaccine in children suffering from hemophilia who had been immunized for the first time in 1993-94 and then in 1996-97. METHODS: In autumn 1996-97, 38 previously vaccinated hemophiliac patients were subcutaneously immunized with a single 0.5-mL dose of subunit influenza vaccine containing the following three virus strains: A/Singapore/6/86 (H1N1), A/Wuhan/359/95 (H3N2) and B/Beijing/184/93 (HB). Antibody response to influenza vaccine was measured before vaccination, 3 weeks after vaccination and 6 months after vaccination, by use of hemagglutinin- and neuraminidase-inhibition tests. To present the level of seroconversion, geometric mean titers of anti-influenza antibodies, mean fold increase, protection rate and conversion rate were determined. All results were compared with the control group of 23 healthy persons who had never been vaccinated against influenza and for whom the same serologic tests were carried out as for the vaccinated group. RESULTS: Three weeks after immunization, antihemagglutinin antibody levels were 3.9-10.9 times higher than before vaccination, but the highest mean fold increase values were recorded 6 months after vaccination, ranging from 8.4 to 28.6. In the case of neuraminidase, mean fold increases of antibodies reached values of 3.6-12.3 three weeks after vaccination and 7.1-29.1 six months after vaccination. The highest proportion of subjects protected was observed 6 months after immunization and ranged from 76.3% to 97.4%, compared to 52.6-60.5% 3 weeks after vaccination. Similar values were obtained for conversion rate: 71.1-86.8% 6 months after vaccination, in comparison with 39.5-42.1% 3 weeks after immunization. CONCLUSIONS: All data obtained in the present study indicate a significant immune response to subunit trivalent influenza vaccine in patients suffering from hemophilia; this is additionally confirmed by the fact that none of the vaccinated children were infected with the influenza virus and no serious adverse reactions were observed after administration of the vaccine.