Evaluation of the Infectivity, Immunogenicity, and Efficacy of Live Cold-Adapted Influenza B/Ann Arbor/1/86 Reassortant Virus Vaccine in Adult Volunteers

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Abstract
A cold-adapted (ca) influenza B reassortant that derived two genes encoding the hemagglutinin and neuraminidase from influenza B/Ann Arbor/1/86 wild-type virus and six internal RNA segments from ca influenza B/Ann Arbor/l/66 virus was evaluated in 66 adult volunteers having a serum hemagglutination inhibition antibody titer ≤1:8. The ca reassortant was attenuated and elicited the production of systemic and local antibodies; the 50% human infectious dose was 106,4 TCID50. Six weeks after vaccination, 12 unvaccinated volunteers and 13 recipients of ca virus (107,5 TCID50) were challenged experimentally with homologous wild-type influenza B virus. The ca vaccine completely protected against illness. and the magnitude of shedding was 50-fold less in vaccinees than in unimmunized controls, fiveof whom became ill. These findings indicate that the six internal RNA segments of the ca influenza B/Ann Arbor/66 donor virus confer desirable properties of a live virus vaccine to a reassortant derived from a virulent virus. Such reassortants may be suitable vaccines for healthy adults.