Why August Is Probably Too Early to Get a Flu Shot

It’s technically still summer, yet pharmacies and schools are already telling us to line up for our flu shots.

But the Centers for Disease Control and Prevention (CDC) recommended today that people get their vaccines for the 2018-19 flu season by the end of October. In other words, two solid months from now.

The exact timing of flu season in the U.S. varies every year, but it’s typically in fullest frenzy in December, January, and February. That’s when you want to make sure you’re best protected. “We know that antibodies peak four to six weeks after getting a vaccine and then slowly go down over the next six months,” explains Ann Falsey, MD, professor of medicine in the infectious disease unit at the University of Rochester Medical Center. “There are some theoretical concerns toward spring that you might be less protected if you get vaccinated too early.”

She advises her patients to get their flu shots in late September or early October–and definitely by Halloween–so they’re protected before flu activity peaks in those winter months. 

You’ll have some measure of protection even earlier, as antibodies–proteins that develop in the blood as part of the immune system’s natural response to potentially harmful invaders like the influenza virus–initially kick in about two weeks after you’re vaccinated.

But timing of the flu season and, therefore, the vaccine, is just one question mark factoring into how effective any vaccine will be. The other is how well the flu strains in the vaccine match what’s actually circulating. And that’s always a bit of a guessing game.

The Southern Hemisphere is still having its flu season (ending more or less next month), and it’s what’s happening there that guides public health decisions up here.

“Experts monitor the strains circulating in the Southern Hemisphere to see what they would predict to circulate in the Northern Hemisphere,” says Dr. Falsey, then vaccine manufacturers get started months in advance. “They have to take their best estimate and pick what strains they think are going to be circulating. Most of the time they get it right, but occasionally the flu can be pesky and a strain can pop up that is divergent,” she says.

Today’s CDC announcement stated that this season’s vaccines have been updated to better match circulating viruses. Last year’s vaccine was not well matched, reducing the effectiveness to about 36%.

“Everybody would love to have 100% efficacy to prevent infection, but that has never been the case,” says Dr. Falsey. “Generally, if you have efficacy in the 50% to 60% range, I think people would be happy with that.” Not only does that prevent some infections, it also cuts down on flu-related complications, including hospitalizations and deaths.

The CDC also announced that the nasal spray flu vaccine will again be available for certain individuals this year after a two-season hiatus. Most vaccines for the upcoming flu season will be quadrivalent, meaning they protect against four different virus strains.

So why are pharmacies and schools pushing vaccines now? It’s possible that the specter of one kid getting sick and then dozens or hundreds following suit is just too terrible to comprehend. Or maybe pharmacies don’t want a stampede of vaccine seekers in October.

The CDC recommends that all individuals age 6 months and older who don’t have a specific reason not to get vaccinated–like a history of allergic reactions to the flu shot–do so. It’s especially important in older adults, who tend to have more and worse complications from the flu, as well as in people who have certain chronic health conditions or who are pregnant.

In addition to pharmacies and schools, you can also get the flu vaccine at your doctor’s office, urgent-care clinics, and many workplaces for free.

Ultimately, there’s really no bad time to get vaccinated. You might be a little early or late, but do it anyway. And ideally, do it around the end of September to the end of October.

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