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Pandemic trH3N2 Vaccine Linked To Minnesota
The two cases from Minnesota occurred in a father (index case) and child. The fatherhad a nasopharyngeal swab positive for swine-origin influenza A (H3N2) virus and had direct swine exposure 6 days before illness onset. The child, whose infection with influenza A (H3N2) virus was confirmed several weeks later by serologic testing, did not have direct swine exposure, and most likely acquired infection from close contact with her father. Other persons in the same household also had ILI during the same period, but serologic results were either negative or inconclusive.
The above comments are from an update of influenza activity in the US (in week 21 MMWR). This week the CDC released sequences from the index case (initially decibed here and discussed here and here) in a construct for a trH3N2 (pandemic H3N2) vaccine from the index case (31M) described above, A/Minnesota/11/2010. The sequences from the index case represented a reassortant, with an H3 closely related to recent trH3N2 sequences (A/Wisconsin/12/2010, A/Pennsylvania/40/2010, A/Minnesota/09/2010), and an N2 distantly related to A/Pennsylvania/14/2010. Most internal genes are closely related to WI/12 and PA/40 which were collected within days of each other and are closely related to each other.
The above Minnesota cluster includes additional family members with ILI (influenza-like illness) as was seen in initial pandemic H1N1 clusters in California in 2009. The second trH3N2 reported in this week’s MMWR may represent an isolate from the Minnesota cluster.
It is likely that the number of trH3N2 cases in the United States is far higher than the confirmed / reported cases.
More detail on trH3N2 cases under investigation would be useful.