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Kong H5N1 Outbreak Signals Vaccine Failure
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 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that H5N1 is evading the outdated vaccine, and may be circulating at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.
at Nature Precedings