Influenza A (H3N2)v (cont.)

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The CDC reported that a reassortment of genetic material from H1N1 and H3N2 viruses resulted in a strain termed influenza A (H3N2)v, where an M gene from H1N1 virus was detected in the H3N2 viruses. New terminology rules, agreed to by the CDC, WHO, and other agencies, resulted in swine-origin influenza viruses found in humans to be called "variant" viruses and should be designated with a "v" after their name. Consequently, the new virus is termed influenza A (H3N2)v.

There have been only 12 confirmed patients with (H3N2)v; six were confirmed to be infected from direct contact with pigs infected with the virus while six others had no recent exposure to any pigs. Because this strain has been detected in at least five states to date, there is some concern it may become widespread. Although this year's trivalent vaccine against the flu contains an H3N2 strain antigen, it is not close enough antigenically to (H3N2)v to provide significant protection. However, people who are older and were infected in the 1990s with the H3N2 virus may have some residual protective immunity to (H3N2)v. The most susceptible human populations to the new virus, according to the CDC, are children, pregnant women, people 65 years of age or older, and patients with chronic diseases (for example, diabetes, asthma, or heart disease). The CDC has reported no deaths from (H3N2)v and suggested that patients be treated similarly to any other flu patients. They also state that the viruses are currently susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).

With only 12 people documented (by rRT-PCR tests confirmed by CDC labs) to have flu caused by (H3N2)v, why the concern? First, there is concern because the USDA Agricultural Research Service have detected at least eight isolates of (H3N2)v in pig populations, suggesting there may be an increasing source for infection of humans. Secondly, about half of the detected (H3N2)v infections were in children without any recent exposure to pigs, suggesting that person-to-person transfer of (H3N2)v can occur. Finally, of all infected people, 11 of 12 were children under the age of 18. The concern is that as the flu season progresses, it may be possible that many more people, especially susceptible children, may become infected, and there is, like in the start of the H1N1 pandemic, no effective vaccine currently available.

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