SAFETY AND IMMUNOGENICITY OF A PURIFIED HEMAGGLUTININ ANTIGEN IN VERY YOUNG HIGH-RISK CHILDREN

Forty-three high-risk preterm children received either one of three doses of purified hemagglutinin antigen (HA) (7.5 mu g/0.25ml, 22.5 mu g/0.25ml or 67.5 mu g/0.25ml) or standard split product vaccine (ST) (22.5 mu g/ml dose) over the 1990-1991 influenza season. Components for all vaccines included A/Shanghai 16/89, A/Taiwan 1/86 and B/Yamagata 16.88. Sera for antibody was drawn before, 6 weeks and 4 months after the first vaccine dose. The study was randomized and blinded. All children received two 0.25 ml doses of vaccine 4 weeks apart. No significant local or systemic reactions occurred. Six weeks after the first dose, children receiving ST vaccine had significantly higher seroconversion rates to A/Shanghai (p=0.03) and to A/Taiwan (p=0.01) than did those receiving equivalent HA vaccine. However, seroconversion rates were significantly higher for those children receiving the highest HA dose. All four vaccine groups responded poorly to B/Yamagata. Geometric mean titres were low for all groups and declined over 4 months. These results suggest that the equivalent dose of HA vaccine offers no advantage over ST vaccine in the immunization of high-risk preterm children.