Testing Two New Seasonal H3N2 Vaccine Targets
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.
at Nature Precedings