New research finds flu shot effective regardless of circulating strains

The flu shot is effective in preventing the flu, even if the circulating strains of the virus do not match the vaccine, according to recent research from St. Michael's Hospital in Toronto.

Researchers reviewed more than 40 years of data from 1971 to 2011, paying special attention to flu seasons in which the flu vaccines were not well matched to the circulating strains. The study found that both the trivalent inactive vaccine for adults and live-attenuated influenza vaccine for children provided significant protection against matched and mismatched flu strains.

"It's quite common for people to say they are not going to get the flu shot this year because they've heard it does not match the strain of flu going around," Andrea Tricco, the lead author of the study, said. "However, we've found that individuals will be protected regardless of whether the flu strain is a match or not."

The vaccines provided protection ranging from 65 percent to 83 percent effectiveness for matched flu strains. The vaccines provided 52 percent to 54 percent protection against mismatched flu strains.

"Looking at matches and mismatches can be a difficult process because it's not a yes or no variable," Tricco said. "Often we're looking at the degree of match between a flu strain and what's included in a vaccine because strains drift from year to year."

The study, which was funded by GlaxoSmithKline, was published in BMC Medicine on Tuesday.