Commentary
Vaccine Resistant H5N1 in Hong Kong
Recombinomics Commentary 23:45
July 7, 2008
The bird flu vaccine used for local chickens is gradually losing its effectiveness, and total failure is not too far away, a leading microbiologist warned yesterday.
This is happening because the H5 virus, which causes bird flu, is shifting further away from the so-called Fujian strain against which the vaccine was originally effective, the University of Hong Kong's head of microbiology, Yuen Kwok-yung, said.
The above comments raise concerns that the vaccination program in Hong Kong is driving H5N1 away from the vaccine. H5N2 is a low path avian influenza and although there will be some cross reactivity, the match will be poor and evolution away from the vaccine will not be difficult.
Reports on H5N1 in China on fecal samples collected between mid 2005 and mid 2006 identified an increase in the Fujian strain (clade 2.3). However, most of the samples were clade 2.3.4 which spread from China into southeast Asia.
However, last year the H5N1 in wild birds in Hong Kong included clade 2.3.2 and the H5N1 in South Korea, Japan, and southeastern Russia was a reassortant with clade 2.3.2 HA and clade 2.3.4 for the other seven gene segments. Reassortants as well as recombinants require co-infections, which can increase in flocks vaccinated with a poorly match vaccine, which keeps the birds healthy, but does not eliminate viral shedding.
The comments above suggest that antibody levels in vaccinated flocks are declining, which may have led to the first reports of H5N1 in poultry in Hong Kong in the past five years.
Use pf poorly matched vaccines leads to rapid evolution. Release of H5N1 sequences from 2007 and 2008 in Hong Kong would be useful.
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