HA A198V substitution reduce the protective efficiency of
inactivated H9N2 avian influenza virus vaccine
To assess the role of HA A198V substitution in immune escape in
vivo , we performed the immunogenic test. The anti-sera in SPF chickens
immunized with the whole inactivated vaccine of the virus F/98 or
rF/HAA198V were collected at 21d after immunization for
the HI assay. The anti-F/98 serum against the F/98 virus was 15.3-fold
higher than that against the rF/HAA198V virus
(P <0.001). The anti-rF/HAA198V serum against the
F/98 virus was 14.4-fold higher than that against the
rF/HAA198V virus (P <0.001). The HI titer of
serum from the chickens vaccinated with rF/HAA198V virus
were lower than that from the chickens vaccinated with F/98 virus
(Figure 5). These data demonstrated that the specific-antibody in serum
induced by the inactivated vaccine of the rF/HAA198Vvirus was lower than that induced by the inactivated vaccine of the F/98
virus. Moreover, the protection efficiency test showed that the antibody
induced by the F/98 vaccine could provide 100% protection against the
challenge by the F/98 virus, and 83.3% protection against the challenge
by the rF/HAA198V virus; while the antibody induced by
the rF/HAA198V vaccine could provide 83.3% protection
against the challenge by either the F/98 virus or the
rF/HAA198V virus (Table 1). These data reveal that the
single A198V mutation
contributes
to immune escape.