Journal of Hygiene

Research Article

Infection with influenza A H1N1: 2. The effect of past experience on natural challenge

J. R. Daviesa1, E. A. Grillia1 and A. J. Smitha1

a1 Influenza Research Unit, PHLS Laboratory, St Lukes Hospital, Guildford, Surrey GU1 3NT


Following its reintroduction in 1978 influenza A H1N1 spread widely in the child population. By the autumn of 1979, 75% of 11-year olds entering a boys' boarding school had detectable antibody. The protective effect of previous experience could be assessed during two outbreaks in the school. In the first outbreak in 1979, 90% of those known to have been infected in the previous year were protected against reinfection. In 1983 after strains of the H1N1 subtype had undergone antigenic drift a large outbreak occurred. It was estimated that past infection conferred protection against clinical influenza in 55%. Where past infection resulted in the presence of antibody which reacted with the outbreak strain the attack rate was further reduced. A large number of sub-clinical infections was detected in all groups.

(Received May 15 1985)

(Accepted June 06 1985)