New trH3N2 Case Raises Pandemic Concerns
Recombinomics Commentary 18:05
August 4, 2011

the two cases reported during 2011, were identified as swine influenza A (H3N2) virus
 
The above comments, from the week 30 MMWR footnote confirm that the novel influenza case reported in the MMWR preview was trH3n2 (pandemic H3N2), but the footnote does not provide any additional information.  The first case reported in 2011 was a case (3F) from Pennsylvania (A/Pennsylvania/40/2010) from a sample collected September 13, 2010.  Thus, it is unclear when the second reported case was infected, and the sequence has not been released, so the relation to the other case reported in 2011 is unclear.

The above case (3F) was infected close to the date of a Wisconsin (A/Wisconsin/12/2010) case (10 month M) who developed symptoms on September 8, 2010, and was announced in a pager alert.  The sequences were closely related, raising concerns the cases in Wisconsin and Pennsylvania signaled human transmission, since there was no reported contact between these cases raising concerns of a large number of unrelated cases. 

These concerns were increased by the second case (31M) from Minnesota (A/Minnesota/11/2010) which was collected on November, 29, 2010 but was closely related to the cases in Wisconsin and Pennsylvania.  Low levels of human transmission would not be easily detected because trH3N2 has human H3 and N2 from the mid-1990’s so serotyping reagents would give results similar to seasonal flu and not indicate a need for further testing, like antigen characterization or sequencing, which would be done at the CDC.

Thus, like the first reported case in 2011, the second 2011 could have been collected months earlier.  Moreover, recent sequences from the CDC came from virus isolated in eggs, which would increase the detection of trH3N2 because of D225G, which is a change that increases affinity for gal 2,3 receptors which are found in eggs, as well as human lung.

Yesterday the CDC released sequences associated with the development of vaccine targets. Included were sequences from the Minnesota case, raising concerns that the number of suspect or confirmed trH3N2 cases in 2011 is significantly greater than the two reported cases.

Additional information, including sequence data on the latest reported case would be useful, as would additional information on other confirmed or suspect trH3N2 cases.

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