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Your Guide To Adult Vaccines

Stay Out of the Hospital With a Flu Shot

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

Woman standing at a pharmacy counter near a flu shot sign.

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En español | Each year, 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 Vaccination 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.

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. The particularly devastating 2017-2018 flu season resulted in 21 million doctor visits, 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. 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.

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. A study published in the New England Journal of Medicine found that the high-dose vaccine was 24 percent more effective in preventing flu in adults 65 and older compared to a standard-dose vaccine. The other option, FLUAD, contains an added adjuvant — a substance designed to “wake up” the immune system, getting it to work harder. Talk to your health care provider about which is right for you.

Now is the time to get your shot

Though some people are opting to get vaccinated early, most doctors still recommend that people aim for no later than October. It's all in the timing, Christensen says: “After you get the shot, it takes about four to six weeks to build immunity against the flu. That generally puts you at Thanksgiving, which is when the virus starts circulating in the U.S. Then you get about six months of immunity out of each flu vaccine before the immunity starts to wane. The flu season goes into March, sometimes April. If people are getting it in August, we worry some of the vaccine's effectiveness will wear off in January and February, when we're at the peak of flu season.”

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, who points to an intriguing (and reassuring) factoid: “Never in modern history have we not had influenza outbreaks in the Southern Hemisphere. But today, in the areas and nations where people are wearing masks, there's almost no influenza.”

The 411 on 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.

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Red Cross workers removing bundles of masks for American soldiers in Boston, Massachusetts, 1918.

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Red Cross workers making masks for American soldiers in Boston, Massachusetts during the 1918 flu pandemic.

Understanding the 1918 Influenza Pandemic Today

Described as the “greatest medical holocaust in history,” the influenza pandemic (more commonly known as the Spanish flu) that began in 1918 lasted for two years, infecting 500 million people worldwide and killing an estimated 20 million to 50 million victims — which, as historians point out, is more than all the soldiers and civilians killed during World War I. The strain was of avian origin. “What is unusual about it is that the genome sequence is genetically distinct,” Poland says. “It was a novel virus, which, of course, is what you need for a pandemic."

Though known as the Spanish flu, it may have been American in origin. The virus started to take hold in the spring of 1918, in the last year of World War I. The Allied and Central Powers nations, afraid that news of the flu would hurt morale, censored coverage of the pandemic. Spain, however, was neutral during World War I, so the press was free to report on the virus. Since the other countries were able to get news of the disease only from the Spanish press, the assumption was that the virus was running rampant in Spain. Eventually — and unfairly — it became known as the Spanish influenza.

In reality, history suggests that the outbreak most likely originated at Camp Funston, part of Fort Riley, near Manhattan, Kansas. “You're crowding tens of thousands of young men into what we call today ‘unsanitary camps’ and shipping them en masse to Europe — depriving them of normal nutrition, sleep, and adding great amounts of stress,” Poland says. “That's all an immune system needs to collapse or overrespond in the face of a novel threat.”

Many of the flu's victims were young and healthy. “One hypothesis is that older people had gotten exposed to some sort of progenitor of that strain decades earlier,” Poland says. “Younger people, however, were immunologically naïve to this virus, and it induced a hyperinflammatory response.”

In the absence of a worthwhile vaccine to prevent the flu, doctors treated it with convalescent human plasma, which appeared to work, though the supply was limited. “They also knew enough about the germ theory of disease to wear masks,” Poland notes. But the medical community experienced much of the same pushback that it deals with today with the coronavirus. “There were people who didn't want to wear masks,” Poland says. “There were city, county and state public health and governing officials who didn't want to cancel patriotic parades and things like that,” and he says those communities often suffered greatly as a result.

Vestiges of the virus remain

Are today's H1N1 viruses descendants of the 1918 virus? “In a sense, yes, because once a virus becomes pandemic, it continues to change,” Poland says. “We don't see the 1918 virus anymore, but we do see vestiges of it.” The H1N1 virus that caused the 1918 pandemic has survived in various forms and has continued to spawn offspring. In fact, the novel H1N1 virus associated with the 2009 swine flu pandemic — which caused 60.8 million illnesses and 12,469 deaths in the U.S. — is considered a fourth-generation descendant of the 1918 virus. (It comes, according to National Institute of Allergy and Infectious Diseases researchers, “from the still-growing family tree of the 1918 virus.")

Current seasonal flu vaccines provide at least some protection from the 1918 H1N1 virus. In fact, Poland says, if you take the 2009 pandemic H1N1 influenza vaccine and immunize mice with it, then expose them to the 1918 virus, they are at least partially protected. There is a cumulative benefit to getting vaccinated year after year. “The influenza vaccine that you and I will get this fall is different from last year's vaccine,” Poland says. “We're training our immune system to recognize these variations and to respond with protective immunity."

A major focus of research is developing a universal flu vaccine that would offer protection against multiple subtypes of flu, rather than selecting and targeting only a few. New seasonal vaccines provide protection against strains predicted to be prevalent during the coming flu season. Not only would a universal flu vaccine eliminate the guesswork and the need to update the vaccine each year, it would shield us from unfamiliar strains that could potentially lead to a pandemic. “The idea is that it would protect against all the of the known influenza viruses,” Poland says. However, he says, “The one thing I've learned after 40 years of studying viruses is we don't know anything yet,” adding that a novel virus might still evade such protection.

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