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Paradigm Shift Intervention Monitoring
Mexico City strengthened its
operational check travelers arriving
Chihuahua and Texas by plane or bus, to avoid an outbreak of influenza.
"We don't want one more death in this situation," said Health Secretary Francisco Osuna.
The above translation suggests that the situation in Mexico is markedly worse than the recently reported deaths would indicate. Confirmation of cases has been problematic. The fatal index case was not confirmed, even though he was the partner of a confirmed case, raising concerns that the H1N1 circulating in Mexico represents a sub-clade that has markedly evolved away from the H1N1 reported in earlier isolates in the United States.
The USDA released a series of pandemic H1N1 sequences from swine in Costa Rica collected in November, 2010 which had significantly evolved away from the pandemic H1N1 sequences. These sequences had a number of changes flanking receptor binding domain position 190, raising concerns that the sequences could jump back into humans and could avoid most of immunity generated against the pandemic H1N1 currently circulating in humans.
The recent outbreaks in Mexico and Venezuela appeared at the end of the flu season for the northern hemisphere. In Mexico, most influenza A had been H3N2, but levels had peaked in late 2010. Recent activity, prior to the current outbreak had been minimal.
The recent cases have produced an unusually high number of severe and fatal cases, which may account for the extraordinary travel checks in Mexico City. Although these types of checks are unlikely to be successful, the implementation of such actions gives the appearance of control, which is also true for the decision to begin a massive vaccination program. Vaccinations were tried in 2009, but had no effect because the seasonal H1N1 was very different from pandemic H1N1.
The same would be true for the Costa Rica swine, which had a large number of receptor binding domain changes. The jump of pandemic H1N1 back to swine allows for dramatic evolution, driven by recombination, as described for the Costa Rican swine.
Release of sequences from the cases in Mexico and Venezuela is now overdue.