Immunogenicity and Protective Effect of Live Cold-Adapted Vaccines against Influenza B after Intranasal Immunization of Mice

Live attenuated («att») vaccines based on cold-adapted («ca») strains are a promising approach of influenza prophylaxis enhancement, however, effectiveness evaluation as well as interrelation with immunogenicity should be elucidated, especially for vaccines against type B influenza.Sterile, pure and concentrated viruses were prepared using a parent wild-type influenza type B and a live «ca» strain derived from the wild-type strain, and their biological activity and phenotype were fully characterized. Mice intranasally immunized twice with the live «ca» vaccines developed sterile immunity (wild-type virus was not isolated in chicken embryos (below limit of detection) from lungs of immunized and subsequently infected mice), however, sera antibodies in hemagglutination inhibition test (HAI) were also not detected (below limit of detection).Live «ca» vaccines against influenza type B viruses are effective, however, protection from infection was not determined by HAI antibodies. Further studies using various methods of immunogenicity evaluation and characterization of mechanisms of protection for influenza vaccines, first of all «att», are needed