Serological Studies on Adult Volunteers Inoculated with Oil-adjuvant Asian Influenza Vaccine

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Abstract
Adult volunteers given a single intramuscular of oil-adjuvant Asian influenza vaccine containing approximately 1/10 the usual antigen content of saline vaccine were selected for long-term serological investigation as part of a large-scale clinical trial by the Medical Research Council. Peak titers of hemagglutination-inhibiting antibody occurred one month after vaccination; 44 (81.5%) out of 54 showed a significant rise in antibody with titers of 1/128 or greater in 34 (64%) subjects. The immune response was greater in persons under 30 than in those over 40. A small proportion of volunteers had a poor antibody response; these consisted of subjects with no evidence of previous experience of Asian virus antigens. One year after vaccine 34 (68%) out of 50 people continued to show antibody titers of 1/128 or above, and after a further 16 months 9 (45%) out of 20 still had titers of this order. Revaccination of part of the group 12 months after the initial dose gave an approximately fourfold increase in mean titer. After four months the antibody levels began to decline at almost the same rate as in non-revaccinated subjects. The immunizing potency of oil-adjuvant vaccine was substantially unchanged after 12 months'' storage at 4[degree] C.