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H3N2 Vaccine Match
the vaccination formula, developed by the Food and Drug Administration in consultation with the Centers for Disease Control and Prevention in Atlanta, appears a good match to fight those strains,
The above comments are widely cited in media reports on the current flu season in the United States. The “good match” generally refers to the H3N2 vaccine target, A/Victoria/361/2011, which replaced A/Perth/16/2009 as the H3N2 vaccine target. Most of the H3N2 circulating in the United States is the Victoria/361 sub-clade, but the week 48 FluView cited two low reactors, and the CDC release of H3N2 sequences from this season identified the two low reactors. The HA sequences of the two isolates identified specific changes which have had role in immunological escape in the past.
The isolate from Hawaii, A/Hawaii/29/2012 had L157S, which is in a region (positions 157-160) which frequently produce low reactors. L157S was circulating in Hawaii prior to the start of the current flu season, and a July isolate, A/Hawaii/22/2012 has been selected by the CDC for testing as an H3N2 vaccine target.
However, the second low reactor, A/Iowa/14/2012, as a change, T128A, which abolishes the glycosylation site at position 126. This change has been seen previously in H3N2 isolates, including the 2004/2005 vaccine target , A/Wyoming/3/2003, for the Fujian H3N2 strain, A/Fujian/411/2002, which caused significant numbers of deaths in those over 65 as well as pediatric cases. The excessive pediatric deaths in the 2003/2004 season led to US regulations that made lab confirmed pediatric deaths in the US reportable. This season there have been 18 pediatric deaths reported in the CDC FluView through week 52, but media reports and state lab reports have cited additional cases.
Moreover, recently release H3N2 sequences by the CDC had T128A in 40% of the isolates from the latter half of November, raising concerns that T128A is becoming dominant and accounts for the dramatic rise in H3N2 cases in December, including the reported pediatric deaths.