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CDC Testing Two New Seasonal H3N2 Vaccine Targets
Recombinomics Commentary 23:20
August 3, 2011

The CDC has released sequences at GISAID indicating it is testing two new seasonal H3N2 vaccine targets, A/Rhode Island/01/2010 X-199 and A/Brisbane/11/2010 X-197 to replace Perth16/2009.  This testing is somewhat unexpected because the vaccine selection committees for WHO as well as the FDA in the United States recommended leaving all three targets unchanged, and the FDA approved use of Perth/16 for the H3N2 target.

The vaccine committee recommendations were controversial, because in the United States the death rate for Pneumonia and Influenza (P&I) deaths was at record levels, which signal immunological escape from prior immunity in the population, which would include immunity due to vaccination.  When the P&I death rate rose to record levels in 2008, all three targets were changed, yet in 2011, all three were recommended to remain unchanged.

The 2011 recommendations were largely based on the antigenic characterization test, which can be heavily manipulated by the reference anti-sera or the isolation of emerging viruses.  The data for the Perth/16 vaccine was highly suspect because the number of low reactors (titers reduced by four fold or more) was on the rise, and the low reactors mapped on multiple branches of phylogenetic trees and sequences that were virtually identical gave opposite results, suggesting most isolate were testing at the cut-off and minor changes in the test assay would show massive vaccine failure, consistent with the high P&I death rate.

The sensitivity and specificity of the assays was also questionable after the fact, because the CDC is currently testing new candidates for all three current targets.  Unfortunately, the vaccine under production for the 2011/2012 season is nearing completion for shipment in the upcoming weeks.

Details of reasons for the testing of new targets for pandemic H1N1, seasonal H3N2, influenza B, and production of a pandemic trH3N2 vaccine would be useful.

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