INDUCTION OF LONG-TERM T AND B CELL MEMORY IMMUNITY TO INFLUENZA A VIRUS (H5N1) IN PERSONS VACCINATED WITH LIVE INFLUENZA A VACCINE (H5N2)

Over last years, a novel strategy for vaccination of people against potentially pandemic influenza A viruses is actively developed worldwide, i.e., a combined (prime-boost) vaccination. It provides amplification (boosting) of immune response for a vaccine be means of pre-vaccination (priming) with another vaccine. We have first studied an issue of immunological consequences for people after priming by live attenuated influenza H5N2 vaccine (LAIV), followed by a boost with inactivated influenza H5N1 vaccine (IIV) 1.5 years later. Unlike non-primed volunteers, the primed persons developed more rapid and high production of serum antibodies (of HAI-, MN-, ELISA-types) after a single vaccination with H5N1 IIV. That concerned induction of antibodies to the H5N1 vaccinal strain A, and other heterologous strains containing H5 haemagglutinin. In primed persons, the antibodies showed higher avidity as compared to non-primed individuals. Before inoculation with H5N1 IIV, the IgG-antibody titers to A virus (H5N1), and the levels of specific CD4+ and CD8+ memory T-cells proved to be higher in primed subjects than in non-primed persons. The boosting effect of H5N1 IIV did not correlate with HAI-and MN-based data on immunogenicity of priming H5N2 live attenuated vaccine. In general, the results obtained justify a new direction in applications of LAIVs for protection against potentially pandemic influenza virus A.