It's only 58% effective against the most common virus out there right now.

By Jessica Migala
Updated January 14, 2020
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One of the best ways to prevent the flu from sidelining you this season is to get the flu shot—that's why you already got yours way back in October, which means you should be pretty much covered this year, right? If only.

According to the newest updated stats from the Centers for Disease Control and Prevention (CDC), there's just a 58% match with B/Victoria viruses—aka, one of the most common viruses out there right now, representing almost 98% of circulating influenza B strains. “It’s not a very good match for B/Victoria,’ said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, reported CNN. "It's not an awful match, but it's not a very good match," he added.

Another less-than-stellar match this season? The flu vaccine is reportedly only a 34% match with influenza A H3N2 viruses—but that strand isn't much of a concern, since it only represents a small percentage of total viruses.

Luckily, this year's flu vaccine is a 100% match with H1N1, which has accounted for about 82% of the influenza A out there. The vaccine is also a 100% match with B/Yamagata, a far less common virus that makes up just 2% of the influenza B circulating.

Okay, so what does all of this mean? How effective is this year's flu shot?

The biggest takeaway here is that this year's flu shot isn't a great match for the leading virus out there right now: B/Victoria—in fact, it's the first time in 27 years that an influenza B virus has dominated the flu season so early on. (Influenza B viruses typically hit in the springtime, on the tail-end of flu season.)

See, that 58% match essentially means that if you (or your child) are exposed to the B/Victoria strain of the flu virus, there's only a 58% chance you'll be protected from it with the flu shot—and there's a 42% chance that you may still get the flu.

Another issue regarding the flu vaccine and its partial ineffectiveness for B/Victoria? Influenza B viruses typically hit children and young adults harder and can be more severe, sometimes leading to hospitalization for complications, or even death. That's especially true this year—21 of the 32 pediatric deaths during the current season being due to influenza B, per the CDC.

But here's the thing about the flu vaccine: It doesn't necessarily give you full protection against the virus—even if it's a good match. Chances that a vaccine will work for you depends on your age and health, as well as if the vaccine matches the circulating viruses out there during the season, says the CDC. A good match means “the antibodies produced by vaccination protect against infection with circulating viruses,” the agency explains.

It happens. After all, no one says the flu vaccine is perfect. Viruses can change—called antigenic drift—in between or during flu seasons, and the vaccine makeup is determined before the season even gets underway. In general, the vaccine is usually 40 to 60% effective, slashing your odds of getting the flu in half if you received the vaccine.

All is not lost, of course, and there’s no reason to get down about the vaccine. Even if you or your children do catch the flu, you’re more likely to get a milder case that you can bounce back faster from, with the flu shot in your system. (If you think that body aches, headaches, and a slightly elevated temperature is bad now…just imagine what could have been, and then pat yourself on the back for getting your vaccine last fall.)

Per CDC estimates, there have been 9.7 million flu illnesses, 87,000 hospitalizations, and 4,800 deaths from the flu so far this season. While we’re in the heart of flu time right now—things peak between December and February—the illnesses can stick around until May. That’s why (if you’re over 6 months old, ahem) you can still get the flu vaccine if you haven’t already. Because a 58% match is way better than nothing.

Oh, and don’t forget to wash your hands after going to the bathroom, before eating, and when you walk in your door after being out in public. And if you’re sick, please, for the love of all that is good, stay home.

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