Flu Shot May Not Match Most Circulating Viruses.

The Los Angeles Times (12/4, Kaplan) “Science Now” blog reports that the CDC issued an announcement on Wednesday saying that only 48% of the viruses being tested now match the strain chosen for this year’s flu shot. Most virus strains that have been tested since October 1 match the virus chosen for the flu shot distributed in South America. The CDC instructs doctors to give patients Tamiflu and Relenza to fight the virus. CDC Director Thomas Frieden will make an announcement on the subject Thursday.

        Reuters (12/4, Steenhuysen) also reports the story, adding that the flu shot is not totally ineffective, as it will continue to fight mutated strains and prevent the most serious complications that can arise from flu infections that would require hospitalization.

        NBC News (12/4, Fox) reports on its website that the CDC explained the mismatch is because the virus has mutated, called drifting, and that this phenomenon is not uncommon. The announcement said, “Though reduced, this cross-protection might reduce the likelihood of severe outcomes such as hospitalization and death. ... In addition, vaccination will offer protection against circulating influenza strains that have not undergone significant antigenic drift from the vaccine viruses (such as influenza A (H1N1) and B viruses).” NBC writes that “vaccinated people may be more vulnerable than usual.”