November 25, 2011
CDC Charade On trH3N2 Swine Exposure Raises Concerns
Posted by: admin : Category: Flu vaccine
The emergence of a trH3N2 human contagion was predicted by sequences from 2010 isolates, which were released after WHO issued a pager alert on two cases (in Illinois and Pennsylvania). The pager alert made some concern, especially in eastern Europe, but the CDC noted that although both cases were H3N2 triple reassortants, sequence differences indicated the trH3N2 was not transmitting in humans.
Similarly, the first reported case with an M gene from H1N1 was from an infection in late July, so the 2011 cases were reported over a 2 month time period prior to the report, and there were 3 more October cases, bring the total number of reported cases to seven over a three month period. Moreover, the first 2011 case had no swine exposure. The CDC speculated that the case was infected by his caretaker, who had swine exposure, but neither the caretaker nor associated swine had symptoms, and no SOIV has been reported in either.
The lack of sub-typing, as well as the absence of two of the four trH3N2 cases from the unsubtypable category raises concerns that the number of trH3N2 samples represented in the table below is markedly higher than the two unsubtypables or the four confirmed cases.
One of the more telling examples was the collection in Pennsylvania, A/Pennsylvania/40/2010, that initially tested as seasonal H3N2. It was determined to be trH3N2 based on subsequent testing which included sequencing. But, the vast majority of seasonal H3N2 samples is not subjected to such additional screening and therefore would be incorrectly designated as seasonal H3N2. Most samples that are PCR tested are samples from patients linked to swine, heavily biasing the association.
One of the more telling examples was the collection in Pennsylvania, A/Pennsylvania/40/2010, that initially tested as seasonal H3N2. It was determined to be trH3N2 based on subsequent testing which included sequencing. But, the vast majority of seasonal H3N2 samples is not subjected to such additional screening and therefore would be incorrectly designated as seasonal H3N2. Most samples that are PCR tested are samples from patients linked to swine, heavily biasing the association.
The lack of sub-typing, as well as the absence of two of the four trH3N2 cases from the unsubtypable category raises concerns that the number of trH3N2 samples represented in the table below is markedly higher than the two unsubtypables or the four confirmed cases.
The finding of the same constellation in a case in Pennsylvania (2F) a few weeks later indicates this virus is transmitting. The Indiana case had contact with a caretaker who had contact with swine. But, those attending state fairs have contact with others who may be transmitting this virus.
This acquisition would lead to more efficient transmission of trH3N2 which bought the M segment from pandemic H1N1. The isolate from the patient in Indiana, A/Indiana/08/2011, has genes that are closely related to the genes of early human cases with trH3N2, but it has also bought the H1N1 MP gene segment. 
