Protection of Infants from Infection with Influenza A Virus by Transplacentally Acquired Antibody

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Abstract
Transplacentally acquired antibody to influenza A virus was measured by a microneutralization test and a radioimmunoprecipitation assay in cord blood obtained from infants at a large urban county hospital in 1975–1978. Random samples tested before epidemic periods were a measure of susceptibility of the population. Twenty-six infants from whom cord sera were available had culture-documented infections with influenza A/Victoria (H3N2) virus when younger than four months. The direct correlation between age at the time of infection and level of antibody measured in cord serum (P < 0.002) suggested a protective effect of transplacentally acquired antibody. None of fourteen acute-phase serum specimens obtained early in the course of culture-positive infections of young infants had detectable antibody to influenza A viral hemagglutinin by the sensitive radioimmunoprecipitation test. Because passively transferred maternal antibody to influenza virus may prevent symptomatic infection in young infants, vaccination of pregnant women could be beneficial.