Vaccination activity of live influenza vaccine in different seasons of the year.

Reactogenicity, immunogenicity and viability of the vaccine virus were studied during vaccination of adults with live allantoic influenza vaccines of the types A (H1N1), A (H3N2) and B in different seasons of the year. Seasonal oscillations of reactogenicity of the vaccines (minimum in summer, maximum in winter) were demonstrated. A decrease in the re-isolation rate of vaccine viruses and in their content in the secretions of the upper respiratory passages was observed in summer. Seasonal oscillations of immunogenicity of the commercial live allantoic influenza vaccine with a marked reduction in its activity in summer were established. The administration of moderately attenuated influenza vaccine viruses in summer results in the production of antibodies up to the level observed in other seasons of the year. Theoretical problems and practical aspects of seasonal oscillations of vaccination activity of live influenza vaccines were studied in connection with the necessity of investigation new vaccine strains in varying seasons of the year.