ATLANTA, Sept. 18 (UPI) -- The influenza strain that caused the most illness last year, H3N2, emerged too late in the season to be included in North American vaccines. This year, however, the flu vaccine is expected to be effective against it based on research by the U.S. Centers for Disease Control and Prevention.
While the vaccine will be effective against known strains of flu, the possibility that an unexpected strain will pop up is very possible, researchers at the agency said. Officials have said, however, that all their testing shows the strains they found circulating most commonly right now in the country are covered by this year's vaccine.
"Get vaccinated," CDC Director Thomas Frieden said at a press conference about the upcoming flu season. "That's the best way to protect yourself, your family and your community against flu."
Last December, researchers correctly called that last year's vaccine would not be as effective as hoped when they saw the A/Switzerland/9715293/2013 flu strain begin to spread. The vaccine turned out to only be about 23 percent effective as a result of the unexpected mutation's emergence after the vaccine had been prepared for the flu season.
While working on this year's vaccine, researchers at the CDC used 199 flu samples collected around the United States between May 24 and September 5. Of those, 118 are H3N2 strains and all of them appeared vulnerable to the new vaccine.
Of the remaining strains researchers collected, 19 were H1N1 strains similar to the one that caused swine flu to spread in 2009 and 2010, 35 are similar to the B/Phuket/3073/2013 strain, and the remaining 26 resemble the B/Brisbane/60/2008 strain. This year's regular trivalent shot is effective against the H1N1 and B/Phuket/3073/2013 strains, while the quadrivalent shot should ward off all three.
"Annual influenza vaccination is the best method for preventing influenza and its potentially severe complications," CDC wrote in its full update on flu and flu vaccine in the United States. "While vaccine effectiveness can vary, vaccination has been shown to reduce influenza illnesses, doctors' visits, influenza-related hospitalizations, and deaths. Even during seasons when vaccine effectiveness is reduced, substantial public health impact can still be measured."