Getting COVID and Flu Shots Together May Slightly Increase Risk of Stroke in Older Adults

Fact checked by Nick Blackmer

• New research from the Food and Drug Administration (FDA) found that getting the COVID-19 vaccine and high-dose flu shot together may increase the risk of stroke in people 85 and older.

• The potential risk is small, so more research is needed for clinical certainty.

• Experts still recommend getting both vaccines, despite the new study’s results.

Getting a high-dose flu shot and COVID-19 vaccine at the same time may slightly raise the risk of stroke for people 85 years and older, according to a new study from the Food and Drug Administration (FDA).

It’s worth noting that the study has not yet been published in a peer-reviewed journal, and experts agree the results should not dissuade people who are eligible for both vaccines from getting them.

“These results in no manner change our very strong recommendation to get vaccinated,” Thomas Russo, MD, an infectious diseases expert at the University of Buffalo Jacobs School of Medicine and Biomedical Sciences, told Health.

Brandon Giglio, MD, the director of vascular neurology at NYU Langone Hospital in Brooklyn, said that the new data hasn't changed his suggestions to patients.

“I would still recommend [both vaccines] to my patients because the benefits of them getting vaccinations most likely outweigh the risks,” Giglio said.

The FDA investigators who worked on the new study were not available for comment, but a spokesperson for the agency reiterated that the vaccines are still considered to be safe and effective in a statement to Health.

The review conducted in the study is simply a piece of ongoing safety surveillance efforts—the benefits still far outweigh the risks.

“The FDA is confident in the safety, effectiveness, and quality of the COVID-19 vaccines that the agency has authorized and approved,” the statement said. “The available data continue to demonstrate that the benefits of these vaccines outweigh the risks.”

Though the data might sound concerning, it’s crucial to contextualize the potential risk outlined in the new report.

“The FDA is being transparent here, which is important,” Russo said. “They’re letting people know the data, but it’s important to realize the uncertainties of this data.”

Here’s what you need to know about the new research, what it means for people 85 and older, and whether or not staggering vaccines may be an effective strategy for minimizing risk of stroke.

Related: What Is the Booster Shot and Why Is It Necessary?

Experts Aren’t Yet Sure the Increased Risk Is Real, Despite the Data

The new study relied on data from Medicare beneficiaries who got a Pfizer or Moderna COVID vaccine, a high-dose flu vaccine, or both together from August 31 to November 6, 2022.

High-dose flu vaccines, technically known as adjuvanted vaccines, are sometimes given to people 65 or older because their immune systems aren’t as strong as those of younger people.

The researchers found that there were three extra cases of transient ischemic attack (TIA), sometimes called “mini-stroke,” per every 100,000 immunizations.

“The differences that we’re seeing were very small and may or may not with future studies prove to be real,” Russo said. “This may be a statistical quirk that doesn’t bear out.”

There was a slightly elevated risk of stroke among people aged 65 to 74 who received the Moderna vaccine. Among people aged 85 and older, the risk increased in those who got the Pfizer vaccine.

That the data did not show an increased risk for people 75 to 84 is unusual—since risk should increase with age—and is one reason to pause before putting too much emphasis on the new findings, Russo explained.

In addition to a very slight increase of TIA among people who got both the COVID and high-dose flu vaccines, the researchers noted a “slightly elevated” risk of stroke in some people who had only gotten a flu shot.

“This finding suggests that the observed risk of stroke in the concomitant subgroup [i.e., people who got both vaccines] was likely driven by influenza vaccination alone rather than concomitant administration,” the study authors wrote.

It’s important to note, Russo said, that there is no proof that the vaccinations are responsible for the TIAs.

“This is an observational study; it does not connote cause and effect,” he explained.

Both COVID and the flu increase the risk of stroke, Giglio said; the elevated risk of stroke after COVID, specifically, can remain up to nine months after the infection has ended.

Both viruses can also cause several other life-threatening complications, particularly in older adults.

Flu has been linked to an increased risk of respiratory failure and heart attack in older adults, Giglio said, while COVID is more likely to cause severe disease in everyone 50 and older. This means they’re more likely to require hospitalization, be admitted to the intensive care unit (ICU), rely on a ventilator, or even die from the virus.

Should You Stagger Your COVID and Flu Vaccines?

Though it’s considered safe to get your COVID and flu vaccines at the same time, you ultimately may be more comfortable staggering them.

Both shots can cause irritating side effects such as redness or swelling at the site of vaccination, muscle aches, and fatigue.

“I would still recommend to my patients that they should get their [vaccinations], but they could definitely separate them by at least two weeks,” Giglio said.

Doing this may make the side effects slightly more palatable since at least you won’t be experiencing them all at once, Russo said.

However, if you live in a rural area, don’t drive, or are otherwise limited in the number of times per month you can visit a vaccination site, you shouldn’t hesitate to get both vaccines at the same time.

“If this is your only opportunity, go for it,” Russo said.

Regardless of When You Get Vaccinated, It’s Important to Know the Signs of a Stroke

Knowing the warning signs of a stroke is a good idea—particularly if you’re a caretaker of older adults—both in the weeks after vaccinations and beyond, Giglio said.

“In our country, even though people might recognize the symptoms of a stroke, they may not treat them as an emergency,” he said.

The Centers for Disease Control and Prevention (CDC) recommends using the acronym FAST to remember stroke symptoms:

• Face: Stroke can cause one side of a person’s face to droop. If you suspect someone may be having a stroke, ask them to smile to determine whether this is happening.

• Arms: Stroke can cause a person’s limbs to drift downward. If you suspect someone may be having a stroke, ask them to raise both arms to compare.

• Speech: Stroke can cause slurred speech. If you suspect someone may be having a stroke, ask them to repeat a simple phrase.

• Time: Time is of the essence when a person is having a stroke, so if you notice any other symptoms, you should act immediately.

Severe headache, numbness, and eyesight problems could also be warning signs, Russo said.

If you notice any of the symptoms, you should go straight to your local emergency room, Giglio said, bypassing any calls to your primary care doctor’s office or even a visit to urgent care.

Not all facilities are equipped to treat stroke, and it’s always good to know which healthcare center you should report to if you suspect one. Going to the wrong facility first will only delay you, because staff will simply direct you to the emergency room, Giglio explained.

While stroke risk should always be studied, the new data aren’t compelling enough to change any vaccination policies we have right now, Russo said.

“The bottom line here is that the differences are so small that it brings into question: Is this a statistical quirk, or is this something real?” Future studies, he said, will be the only way to tell.

Related: Stroke Deaths Expected to Increase 50% By 2050—Here's How to Lower Your Risk

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