Submitted to: European Scientific Working Group on Influenza
Publication Type: Abstract only
Publication Acceptance Date: 5/1/2002
Publication Date: 5/1/2002
Citation: Subbarao, K., Chen, H., Murphy, B., Cox, N., Swayne, D.E., Matsuoka, Y. 2002. Development And Evaluation Of Candidate Influenza A Vaccines For Pandemic Preparedness. European Scientific Working Group on Influenza. Interpretive Summary:
Technical Abstract: Aquatic birds can be infected by influenza A viruses of 15 hemagglutinin (HA) and 9 neuraminidase (NA) subtypes and serve as a reservoir from which novel influenza subtypes can be introduced into humans and cause a pandemic. The observations that avian H5N1 and H9N2 influenza A viruses infected humans in Hong Kong and China and continue to circulate among birds in the region raise concerns that these subtypes have the potential to cause a pandemic. Licensed vaccines are not available to prevent human infections by avian influenza A viruses. Currently licensed human influenza vaccines are formalin-inactivated vaccines that are prepared from seed viruses containing HA and NA genes of epidemic strains in a background of internal protein genes derived from the vaccine strain, A/Puerto Rico/8/34 (PR8). Reassortant H1N1 and H3N2 human influenza A viruses with the internal protein genes of A/Ann Arbor/6/60 (H2N2) cold adapted (AAca) virus have been tested extensively in humans and have proven to be attenuated and safe as live virus vaccines; the ca, attenuation and temperature sensitive (ts) phenotypes of the AAca virus are conferred on the reassortant vaccines by the internal genes of the AAca virus. To prepare seed lots of vaccines to protect humans against potential pandemic strains of avian influenza, we generated four H5 and H9 reassortant viruses by plasmid-based reverse genetics or classical reassortment, in a background of PR8 or AAca genes. The parent avian influenza A viruses from which the HA and NA genes were derived were A/Hong Kong/491/97 (H5N1), A/chicken/Hong Kong/G9/97 (H9N2) and A/pheasant/NJ/1355/98 (H5N2). The genotypes of the reassortant candidate vaccine viruses were confirmed by sequence analysis. Analysis of post-infection ferret sera established that the antigenicity of the avian HAs were preserved in the reassortant viruses. Reassortant viruses bearing the internal protein genes of the AAca virus displayed ts and ca phenotypes. The vaccine candidate viruses replicated poorly in chickens and were not highly pathogenic for chickens. The presence of PR8 or AAca virus genes did not enhance the virulence of the reassortant viruses in BALB/c mice, compared to the parent avian influenza viruses. In summary, we have utilized reverse genetics and reassortment techniques to generate four H5 and H9 reassortant viruses in a background of two different vaccine viruses. These viruses bear biological properties that are desirable in candidate vaccines. The generation and evaluation of these reassortant viruses as seed viruses for vaccines are important steps in pandemic preparedness.