But even though the flu shot has been around since the 1940s, and has been proven every year since to be the most effective way to prevent infection with the influenza virus, there are lots of misunderstandings and misconceptions about it. Whether you’re a fan of the flu shot and never miss a season, you’re wary of it, you simply forget about it, or you figure you won’t get sick — and if you do, it won’t be so bad — learning all you can about the vaccine can help you make informed decisions about it going forward. Twice a year, representatives from five of the top participating centers come together to review data and recommend which strains to include in the upcoming flu vaccine. “These flu experts try to anticipate what the dominant strains are going to be nine months down the road,” explains William Schaffner, MD, professor of infectious disease at Vanderbilt University School of Medicine in Nashville. “They’re often on target, but on some occasions, the flu virus that circulates varies from the vaccine. How effective the influenza vaccine is changes from year to year too.” In other words, flu virus experts have to base their recommendations on a moving target, which means the flu vaccine can’t be perfect. Even so, according to the Centers for Disease Control and Prevention (CDC), the most recent research suggests the flu shot lowers the risk of illness from 40 to 60 percent. As for the specific influenza strains included in the flu vaccine, for the 2022-2023 season, there are four: two influenza A strains and two influenza B strains. In previous flu seasons, most vaccines protected against only three strains.
