Several researchers said that the main circulating influenza strain in the United States has mutated, noting that vaccines may not prevent infection. According to a pre-print study (pdf) led by Scott Hensley, a professor of microbiology at the University of Pennsylvania, flu shots do not protect against a mutated variant of the H3N2 influenza virus, or the most common one, as vaccines do not match the strain well anymore. “From our lab-based studies it looks like a major mismatch,” Hensley told CNN on Thursday. He noted that his study covered only H3N2, adding that the vaccines are supposed to protect against H3N2, H1N1 and two strains, of influenza B. “We have been monitoring this virus for several months,” he said, noting that influenza viruses mutate constantly. The new H3N2 strain includes changes that allow it to evade antibodies that that body creates in response to the vaccines, he told the network. The Centers for …