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Stay Out of the Hospital with a Flu Shot

Timing and dosage can be key; here's what to ask for

spinner image Woman standing at a pharmacy counter near a flu shot sign.
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Each year, about one-third of adults 65 and over don’t get an influenza vaccine. It’s a troubling statistic, says Gregory Poland, M.D., an infectious disease expert and director of the Mayo Clinic Vaccine Research Group: “If someone asked me, ‘What could I do that would increase the chances that I would not live through Christmas?’ I’d say, ‘Don’t wear your seat belt, don’t get a flu vaccine, and ignore the COVID recommendations.’”

Indeed, an annual flu vaccine is crucial. “We need it annually because the [virus] strains are slightly different each year,” says Kristin Christensen, M.D., an internal medicine specialist affiliated with Penn Medicine, in Philadelphia. Researchers try to predict what will be the most prevalent strains in any given flu season and update the vaccine accordingly; this year, every vaccine that’s available will protect against four strains of influenza.

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The vaccination is especially important for older adults, whose immune systems naturally weaken with age. This puts them at high risk of developing serious complications from flu, particularly pneumonia, which can be life-threatening. According to the CDC, in recent years about 70 to 85 percent of seasonal flu-related deaths have occurred in people 65 years and older, and 50 to 70 percent of hospitalizations have occurred among those in this age group.

What’s more, says Poland, “An older person hospitalized with influenza runs about a 12-fold increased risk of heart attack and about a sixfold increased risk for stroke,” since flu increases the risk of these cardiovascular events.

The particularly severe 2017-2018 flu season resulted in 810,000 hospitalizations and 61,000 deaths in the U.S. Sixty-seven percent of hospitalizations occurred in people age 65 and older that season; they also accounted for 83 percent of deaths. 

Last flu season, of course, was different. Rates of influenza during the 2020-2021 season were significantly lower than usual. For one thing, COVID-19 precautions — such as masks and social distancing, working from home, and reduced international travel — meant fewer opportunities for the flu to spread.

Now that people are returning to a more “normal” life — ditching their masks, returning to offices and schools, gathering at sporting events, hopping on planes — health care experts warn that the virus could very well return to pre-pandemic levels. 

Lower immunity levels from last year’s nearly nonexistent flu season could also hurt us. “Since there was no flu last year, we don’t have any of that natural acquired immunity in our population this year. So that just means we have many more people susceptible which could fuel transmission if and when the season really picks up steam,” says Lauren Ancel Meyers, an epidemiologist at the University of Texas at Austin and director of the UT COVID-19 Modeling Consortium.

Which shot to get

Those 65 and older should get one of two vaccines specifically targeting their vulnerable age group: Fluzone High-Dose and FLUAD. Fluzone High-Dose gives you four times the amount of influenza antigens — the part of the vaccine that helps your body build up protection against flu viruses — compared to the standard dose. The other option, FLUAD, contains an added adjuvant — a substance designed to boost your immune response. Talk to your health care provider about which is right for you.

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A flu shot can also help you avoid pneumonia, another respiratory infection that can sometimes piggyback on a system weakened by flu. According to new research, people who got a flu shot earlier this year may be less likely to suffer a severe COVID-19 infection down the road. In one such study, published in the journal Plos One, researchers analyzed the electronic medical records of 74,754 people who tested positive for COVID-19 and found that those who had gotten the flu vaccine during the previous six months were less likely to have had health complications related to their COVID-19 infection.

Doctors typically recommend getting your shot between September and the end of October. Meyers recommends getting your shot on the earlier side this year, where possible. “We don’t know exactly if, when, or how large or how severe this flu season is going to be. But with RSV [respiratory syncytial virus], we saw an unusually early surge in transmission, and the same might happen with flu. Because of that uncertainty, people should absolutely vaccinate, and vaccinating early could provide more protection for individuals and for communities regardless of if and when the virus starts spreading widely.”

In terms of timing, Christensen notes it’s also important to consider when you’ll receive the flu vaccine’s full protection. “After you get the shot, it takes about four to six weeks to build immunity against the flu. Then you get about six months of immunity out of each flu vaccine before the immunity starts to wane.” For this reason, he says, getting your shot in, say, August, could be too early, since protection could wear off while flu is still widespread.

Even if you’re vaccinated, there’s a possibility you could get the flu. You may be exposed to a virus that is not included in the seasonal flu vaccine, since many different flu strains circulate every year. (The overall effectiveness the vaccine ranges from 40 to 60 percent during the years when the vaccine and flu strains match.) 

“We decide on which strains are going to be in the vaccine no later than February or March. But by the time October and November come around, you can have a new influenza virus that is the predominantly circulating strain,” Poland says. “The public might say, ‘The vaccine didn’t work.’ Well, they’re right. But it’s because the virus changed.” Even so, a flu vaccination may lessen the severity of illness if you do get sick. A 2017 study found that the vaccine reduced deaths, ICU admissions and the length of hospital stays among flu patients.

And know this: “Wearing masks, as well as practicing social distancing and hand sanitation, are as effective for the flu as they are for the coronavirus,” says Poland.

What to know about the flu vaccine

Who needs it: All adults, no matter what their age. Be sure to let your health care provider know if you’ve had a severe reaction to the flu shot in the past, are allergic to eggs (the flu vaccine is most commonly grown in them) or have (or have had) Guillain-Barré syndrome (GBS). On rare occasions, people may develop this disorder, in which the body’s immune system damages nerve cells, causing muscle weakness and sometimes temporary paralysis in the days or weeks after getting the vaccination. (Studies suggest, however, that it’s more likely that a person will get GBS after getting the flu itself rather than the vaccination.) If you have a fever, you’ll likely be asked to wait until your temperature is back to normal before you get the vaccine.

How often: Once a year (the sneaky virus itself changes every year). Flu season typically begins in October and ends in March; the CDC recommends rolling up your sleeve by the end of October, since it takes about two weeks after a vaccination for flu-fighting antibodies to develop in the body.

Why you need it: The flu can lead to hospitalization and sometimes death — and older adults are the most vulnerable. Studies show that a vaccination can reduce the risk of falling ill by as much as 40 to 60 percent.

What’s Ahead: Flu + Covid Shots

Experts tell us it’s safe — as well as potentially time-saving — to get any upcoming COVID booster shot at the same time as your flu shot. What’s more, drug companies are currently working on combination vaccines designed to (down-the-road) tackle the flu and COVID, two very different viruses, in a single dose. Vaccine developer Novavax has combined its flu vaccine, NanoFlu — still in the testing phase — with the COVID-19 vaccine. The shot produced antibodies against both viruses. Moderna is also developing a vaccine targeting both flu and COVID-19 — with plans to develop a “triple-whammy” respiratory vaccine that combines seasonal flu, COVID-19 and respiratory syncytial virus (RSV) protection with a single injection. And Sanofi and Translate Bio have started a trial of a mRNA flu shot which targets a particularly nasty strain of the virus — H3N2 — associated with more severe illness, especially among those considered at-risk, such as older adults and younger children.

Editor’s note: This article was updated in September 2021 with new information about the 2021-2022 flu season. 

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