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Paradigm Shift Intervention Monitoring
Confirm West Virginia H3N2v
The above comments are in the California Department of Public Health December 15 advisory. The West Virginia cluster was described in the CDC early release MMWR, but the 23 ILI cases were not mentioned.
The earlier report is in tomorrow’s MMWR. The description of the cluster makes it clear that the trH3N2 was at the Mineral County day care center was circulating for a month, but only two samples were tested, in spite of the large number of ILI cases and high attack rate.
Although sequences from all eight gene segments for the index case (1M – A/West Virginia/06/2011) were released, only the HA and NA sequences were released for the contact (3F – A/West Virginia/07/2011), which supported transmission because the HA sequences were identical, and there were only 2 differences in the N2 sequence, which was distinct from the N2 from the first 10 trH3N2v cases (H3N2pdm11) reported in 2011.
GISAID just released a partial MP sequence from the contact and it was an exact match with the index case (see list of top 100 GISAID matches here). Thus, the only exact match for the HA and MP sequences from the West Virginia contact are the West Virginia index case, confirming transmission.
The high attack rate may be linked to the N2, which is concentrated in trH3N2 swine sequences (in contrast to the ten prior H3N2v cases in 2011, which are linked to trH1N2 swine sequences, although both lineages trace back to seasonal H3N2 from 2003).
The two N2 sequence from the West Virginia cluster have two tandem polymorphism, L370S and S372L which are in seasonal H3N2, and may signal further adaptation to humans