Submitted to: Options for the Control of Influenza Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2007
Publication Date: June 17, 2007
Citation: Suarez, D.L., Pfeiffer, J., Nguyen, T., Pantin Jackwood, M.J. 2007. Vaccine efficacy against challenge with HPAI H5N1 virus isolates from Vietnam [abstract]. In: Options for the Control of Influenza VI Conference, June 17-23, 2007, Toronto, Canada. p. 34. Technical Abstract: Multiple isolates of H5N1 were isolated from northern Vietnam in December of 2005. All the viruses characterized were clade 2 viruses, but phylogenetically they formed two separate sub-lineages. The isolation of clade 2 viruses was unexpected, since previous isolations from both northern and southern Vietnam were clade 1 viruses. Viruses from both lineages killed chickens within two days in experimental inoculations, and were also highly virulent for 2-week old Peking ducks, killing them within four days of challenge. Two representative viruses from each lineage were selected for further antigenic and vaccine efficacy studies. Comparison of cross hemagglutination inhibition titers showed marked differences in titer when using homologous and heterologous antigen. For the vaccination efficacy study, 2-week old white leghorn chickens and 1-week old Peking ducks were vaccinated with one of four oil emulsion vaccines, two of which are commercial vaccines currently used in Vietnam. Three weeks later, these birds were challenged intrachoanally (intranasally) with log10 to the 6th EID50 of one of two viruses each belonging to a different lineage. All four vaccines provided clinical protection for most vaccinated birds, but differences in antibody titer were seen between vaccines. Oropharyngeal virus shedding was compared by real-time RT-PCR to evaluate shedding among the different groups. All sham vaccinated birds died within 2 days. By compiling the data from these various analyses of the recently isolated Vietnam highly pathogenic H5N1 viruses, we will gain knowledge which can be applied to selecting vaccine seed strain viruses in the future.