Live attenuated influenza virus vaccine trial in children.

Thirty-four children received intranasally a live attenuated influenza A virus vaccine, and were then followed for six months to evaluate the vaccine safety, immunogenicity, and efficacy. All but one of the 31 children with hemagglutination inhibition (HI) titers less than 64 before inoculation responded with at least a four-fold rise in antibody titer to a single dose of vaccine. One child required two doses. Seven (21%) of the vaccinees also responded with production of nasal neutralizing antibody. The vaccine was well tolerated with few clinical reactions. Two vaccinees developed fever possibly attributable to the vaccine. No transmission of the vaccine virus to any of the 25 unvaccinated contact children was demonstrable. Five months after this vaccine trial an influenza epidemic due to a heterologous influenza A strain occurred in the community. During this outbreak acute febrile and/or respiratory illness occurred in 12 or 52% of the contact controls, and in six or 19% of the vaccinees. In two of these six vaccinees, influenza A infection was confirmed by at least a four-fold increase in HI titer. This study suggests this study suggests that this vaccine is safe, easily administered, highly immunogenic in children, and is protective against a heterologous strain epidemic in the community.