Hong Kong H5N1 Outbreak Signals Vaccine Failure
Recombinomics Commentary 13:59
December 10, 2008
SAR's biggest chicken farms - Fung Kong Tsuen in Yuen Long - revealed that 200 of its birds had dropped dead.
A number of the dead chickens had been inoculated against the flu, sparking concerns over the efficacy of the vaccine and a possible mutation of the virus.
The above comments regarding the H5N1 outbreak on a large Hong Kong farm again raises concerns of a vaccine failure. These concerns were raised over the summer when H5N1 was detected in a number of live markets in Hong Kong (see updated map). The vaccine in use in Hong Kong is directed against low path H5N2 in circulation 10 years ago, and has been losing effectiveness as H5N1 evolves.
A large number of H5N1 sequences from the 2007/2008 outbreak in wild birds in Hong Kong have been released (see list here here here here here) and these sequences are two Fujian sub-clades (2.3.2 and 2.3.4) in HA although the other seven gene segments are largely 2.3.4. Human cases have been reported in Shenzhen and Guangdong and those sequences were 2.3.4. However, the HA 2.3.2 sequences migrated to the north last spring and were found in whooper swans in Japan as well as outbreaks in South Korea and Russia. A culler/soldier in South Korea was symptomatic and was H5 PCR confirmed, although South Korea denied that he was H5N1 infected (but he promptly recovered after treatment with Tamiflu).
The presence of H5N1 in vaccinated flocks on a farm in Hong Kong, as well as wet markets in Hong Kong during the summer, raises concerns that H5N1 is evading the outdated vaccine, and may be circulating at low levels due to partial immunity in vaccinated flocks.
Release of sequence data from the H5N1 outbreaks over the summer, as well as the current outbreak, would be useful.
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