Benefits and Side Effects of the Flu Vaccine

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Randomized placebo-controlled trials show that flu shots can be extraordinary lifesavers.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Intro: In this three-video series, I show the science behind the pros and cons of the flu vaccine, pneumonia vaccine, and shingles vaccine. 

Every year, influenza typically kills between 4,000 and 20,000 Americans––though the death toll for the 2017 to 2018 season was estimated at 80,000, making it one of the deadliest in the last half century. Most hospitalizations and 90 percent of flu-related mortality occur in those age 65 and older (and most over the age of 75). Mortality rates for the flu at ages 75 and older are 50 times higher than those below age 65. Nonetheless, the CDC recommends everyone over the age of six months get a routine annual flu shot every year––if for no other reason than to help prevent transmission to the more vulnerable. The cruel irony is that older adults—the ones who need protection the most—acquire less robust protection from flu shots, due to waning immunity with age.

Depending on the season, vaccination typically reduces the risk of getting the flu by about 40 to 50 percent. So, in healthy adults, we can say with moderate certainty we can decrease the risk of getting it from like 2 percent each year down to just under 1 percent. Among older adults, even if you get a similar relative risk reduction—from 6 percent down to 2.4 percent—since the risk is higher and the consequences greater, the absolute benefits are greater too.

In the Northern Hemisphere, the flu season can start as early as September, and go as late as March. The problem with getting vaccinated too early in the season is that immunity might wane before the season is over, especially in older adults. So, it might be good to wait until October. But getting it at any time throughout the season is preferable to not getting vaccinated at all.

Yes, the influenza vaccine can cause Guillain-Barré syndrome, an autoimmune attack on your nerves that can leave you paralyzed for weeks—but so too can getting the flu. There are may be one to two additional cases of Guillain-Barré per million vaccinations, versus about 17 extra cases per million contacts with the flu virus. So, you’re much more likely to be temporarily paralyzed by the flu than the flu shot. But since it takes vaccinating about 30 older people to prevent one case of the flu, getting vaccinated would still, in expectation, raise your overall Guillain-Barré risk. But the reason flu shots are recommended is not to lower risk of some obscure autoimmune syndrome, but to reduce the common, and potentially devastating, impacts of the flu that extend well beyond just the respiratory infection.

In the week following a confirmed flu infection, the risk of having a heart attack shoots up six-fold. The inflammation of infection can destabilize atherosclerotic plaques, constrict arteries, and make the blood more liable to clot. So, might flu vaccinations save lives in more ways than one? That’s why indirectly, the flu may kill up to three times more.

Those who get their flu shots are indeed less likely to die from cardiovascular disease in a given year, as well as all causes put together. In other words, those who get regular flu shots live, on average, longer lives. But, who disproportionally gets flu shots? White, married, nonsmokers of a higher social class, with higher education, higher incomes, and health insurance. You can’t tell if it’s truly cause-and-effect until you put it to the test.

There have been four randomized controlled trials—flu shots versus placebo shots—in those with pre-existing heart disease, and overall, those who got the real shots had a 56 percent lower chance of dying from cardiovascular disease, and a 47 percent lower chance of dying from all causes put together. So, flu shots really can be an extraordinary life-saver. Whether the observational data showing fewer deaths across the board—even including those without pre-existing heart disease—similarly pans out is, as of yet, unknown. But, if you notice, for secondary prevention the randomized controlled trials showed even more protection than the observational studies hinted at.

Given the benefits, overcoming vaccine hesitancy should be as simple as correcting misinformation. But sadly, debunking vaccine myths can actually backfire. Busting the myth that inactivated flu shots (the type given to older adults) can give you the flu surprisingly makes people even less likely to get it. Similarly, correcting the falsehood that MMR vaccines cause autism, or that pertussis vaccination causes as many side effects as people think, paradoxically makes people less inclined to vaccinate. The researchers conclude “correcting vaccine myths may not be an effective approach to promoting vaccination.”

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Intro: In this three-video series, I show the science behind the pros and cons of the flu vaccine, pneumonia vaccine, and shingles vaccine. 

Every year, influenza typically kills between 4,000 and 20,000 Americans––though the death toll for the 2017 to 2018 season was estimated at 80,000, making it one of the deadliest in the last half century. Most hospitalizations and 90 percent of flu-related mortality occur in those age 65 and older (and most over the age of 75). Mortality rates for the flu at ages 75 and older are 50 times higher than those below age 65. Nonetheless, the CDC recommends everyone over the age of six months get a routine annual flu shot every year––if for no other reason than to help prevent transmission to the more vulnerable. The cruel irony is that older adults—the ones who need protection the most—acquire less robust protection from flu shots, due to waning immunity with age.

Depending on the season, vaccination typically reduces the risk of getting the flu by about 40 to 50 percent. So, in healthy adults, we can say with moderate certainty we can decrease the risk of getting it from like 2 percent each year down to just under 1 percent. Among older adults, even if you get a similar relative risk reduction—from 6 percent down to 2.4 percent—since the risk is higher and the consequences greater, the absolute benefits are greater too.

In the Northern Hemisphere, the flu season can start as early as September, and go as late as March. The problem with getting vaccinated too early in the season is that immunity might wane before the season is over, especially in older adults. So, it might be good to wait until October. But getting it at any time throughout the season is preferable to not getting vaccinated at all.

Yes, the influenza vaccine can cause Guillain-Barré syndrome, an autoimmune attack on your nerves that can leave you paralyzed for weeks—but so too can getting the flu. There are may be one to two additional cases of Guillain-Barré per million vaccinations, versus about 17 extra cases per million contacts with the flu virus. So, you’re much more likely to be temporarily paralyzed by the flu than the flu shot. But since it takes vaccinating about 30 older people to prevent one case of the flu, getting vaccinated would still, in expectation, raise your overall Guillain-Barré risk. But the reason flu shots are recommended is not to lower risk of some obscure autoimmune syndrome, but to reduce the common, and potentially devastating, impacts of the flu that extend well beyond just the respiratory infection.

In the week following a confirmed flu infection, the risk of having a heart attack shoots up six-fold. The inflammation of infection can destabilize atherosclerotic plaques, constrict arteries, and make the blood more liable to clot. So, might flu vaccinations save lives in more ways than one? That’s why indirectly, the flu may kill up to three times more.

Those who get their flu shots are indeed less likely to die from cardiovascular disease in a given year, as well as all causes put together. In other words, those who get regular flu shots live, on average, longer lives. But, who disproportionally gets flu shots? White, married, nonsmokers of a higher social class, with higher education, higher incomes, and health insurance. You can’t tell if it’s truly cause-and-effect until you put it to the test.

There have been four randomized controlled trials—flu shots versus placebo shots—in those with pre-existing heart disease, and overall, those who got the real shots had a 56 percent lower chance of dying from cardiovascular disease, and a 47 percent lower chance of dying from all causes put together. So, flu shots really can be an extraordinary life-saver. Whether the observational data showing fewer deaths across the board—even including those without pre-existing heart disease—similarly pans out is, as of yet, unknown. But, if you notice, for secondary prevention the randomized controlled trials showed even more protection than the observational studies hinted at.

Given the benefits, overcoming vaccine hesitancy should be as simple as correcting misinformation. But sadly, debunking vaccine myths can actually backfire. Busting the myth that inactivated flu shots (the type given to older adults) can give you the flu surprisingly makes people even less likely to get it. Similarly, correcting the falsehood that MMR vaccines cause autism, or that pertussis vaccination causes as many side effects as people think, paradoxically makes people less inclined to vaccinate. The researchers conclude “correcting vaccine myths may not be an effective approach to promoting vaccination.”

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

Stay tuned for the next two videos, which examine the benefits and side effects of the pneumonia and shingles vaccines. 

Can you prevent the flu with foods and supplements, like elderberry and echinacea? See Elderberry Benefits and Side Effects: Does It Help with Colds and the Flu?.

I don’t have many other videos on the flu, but here are a few on preventing and treating colds:

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