Abstract
To prevent H9N2 avian influenza virus infection in chickens, a long-term vaccination program using inactivated vaccines has been implemented in China. However, the protective efficacy of inactivated vaccines against antigenic drift variants is limited, and H9N2 influenza virus continues to circulate in vaccinated chicken flocks in China. Therefore, developing a cross-reactive vaccine to control the impact of H9N2 influenza in the poultry industry remains a high priority. In the present study, we developed a live cold-adapted H9N2 influenza vaccine candidate (SD/01/10-ca) by serial passages in embryonated eggs at successively lower temperatures. A total of 13 amino acid mutations occurred during the cold-adaptation of this H9N2 virus. The candidate was safe in chickens and induced robust hemagglutination-inhibition antibody responses and influenza virus–specific CD4+ and CD8+ T cell immune responses in chickens immunized intranasally. Importantly, the candidate could confer protection of chickens from homologous and heterogenous H9N2 viruses. These results demonstrated that the cold-adapted attenuated H9N2 virus would be selected as a vaccine to control the infection of prevalent H9N2 influenza viruses in chickens.
Highlights
The H9N2 avian influenza virus (AIV) was first identified in chicken farms in Guangdong Province of China in 19921
When compared with inactivated vaccines, live attenuated influenza vaccines (LAIVs) can elicit a broader range of virus-specific immune responses, including mucosal, serum antibody and cell-mediated responses, increasing the likelihood of generating broadly cross-reactive responses that may be effective against multiple virus strains[21]
H9N2 viruses isolated in Korea are phylogenetically and antigenically distinct from those viruses circulating in China[32]
Summary
The H9N2 avian influenza virus (AIV) was first identified in chicken farms in Guangdong Province of China in 19921. To prevent H9N2 avian influenza virus infection in chickens, a vaccination program using inactivated oil-emulsion vaccines has been ongoing in China since 19984. At least four different antigenic groups have been identified among H9N2 viruses in chickens in China, resulting in failure of immunization by inactivated vaccines[4,16,17,18]. Developing live attenuated vaccines conferring protection against antigenic drift variants would be a better choice to control H9N2 influenza in poultry, in China. In Korea, a cold-adapted attenuated H9N2 A/chicken/Korea/S1/03 vaccine strain was developed and experimentally shown to protect against wild type virus challenge[29]. Protective efficacy of the cold-adapted virus against wild H9N2 influenza viruses belonging to different HA lineages circulating in China was evaluated
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