Early assessment of the current flu vaccine’s ability to protect against circulating strains of the virus has left some health officials wondering if a successful match corresponds to better protection.
Public health officials assured the public that the vaccine is a good match for the circulating strains of the virus for the 2012-2013 season. According to U.S. data, the vaccine is approximately 55 percent effective in protecting against influenza A infection and 70 percent effective in protecting against influenza B infection, the Canadian Pressreports.
In 2012, Michael Osterholm, the director of the Center for Infectious Diseases Research and Policy at the University of Minnesota, published a report on the influenza vaccine and its shortcomings. It showed that a good vaccine match does not guarantee better protection. On the flip side, a bad vaccine match did not prove to be an ineffective vaccine.
“The more we’ve peeled back this onion called the match, the more we realize we have many questions about it that we can’t answer,” Osterholm said, according to the Canadian Press. “I would not base whether I get influenza vaccine on what the match is. I would just get it.”
Until recently, experts estimated that flu vaccines reduced the risk of being infected by between 70 to 90 percent. During the 2009 H1N1 pandemic, the vaccine only had a 56 percent effectiveness. That vaccine was also well matched to the circulating strains.
The U.S. Centers for Disease Control adjusted its estimate of flu vaccine effectiveness to between 50 and 70 percent, with an effectiveness estimate of 62 percent for the current season.
“I think having vaccine effectiveness of 60 percent overall is very reasonable,” Nancy Cox, the head of the CDC’s influenza division, said, according to the Canadian Press.
Edward Belongia, the director of the epidemiological research center at the Marshfield Clinic in Marshfield, Wis., said that determining if a vaccine is a good match may not be enough data to determine effectiveness, the Canadian Press reports.
“So it’s not sufficient to say there’s a good match or there’s less than a good match,” Belongia said, according to the Canadian Press. “And in fact there are some seasons where the match is reported to be not ideal, and yet they still get vaccine effectiveness estimates in the same general range…(Having a good match) is certainly a factor. But it’s not the only factor. And I think we don’t understand all the factors that are driving clinical vaccine effectiveness.”