A variant influenza virus that has infected a dozen people since August 2011 -- almost all under 10 years of age -- is less of a threat to adolescents and adults, because they show some cross-reactive antibody to it, according to an MMWR article. All cases recovered fully.
The variant, called influenza A (H3N2)v, carries genes from avian, swine, and human viruses. There is evidence that it is transmissible from person to person.
The CDC reports that roughly a third of people over age 10 have cross-reactive antibodies to this virus "that might provide some protection from infection." The proportion is slightly less in those aged 65 and older.
If the virus starts to show sustained person-to-person transmission, the CDC says a specific vaccine virus has been isolated and could be used to develop a vaccine.
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