Why you shouldn't worry about a connection between Bell's palsy and COVID-19 vaccines

"At this point, there's no evidence to support that these vaccines trigger an increased risk of Bell's palsy," an ear, nose & throat specialist said.

• Both Pfizer and Moderna's vaccines have been vetted by the FDA, and so far they look very safe and effective at preventing COVID-19 infections, based on trials in tens of thousands of volunteers around the world.
• Common side effects after vaccination have included arm pain, fatigue, and headaches, which last a few days, but no major safety concerns have been raised yet. 
• Still, some concern has been voiced about a potential connection between the vaccines and Bell's palsy, a temporary facial paralysis, after 7 cases of the condition were reported among vaccine recipients. 
• "At this point, there's no evidence to support that these vaccines trigger an increased risk of Bell's palsy, it's really important for the public to understand that," one otolaryngologist said. 
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By now, hundreds of thousands of people around the world have gotten injections of Pfizer's new COVID-19 vaccine, which was deemed both safe and effective enough for a Food and Drug Administration emergency use authorization during the pandemic.

Before the shot was released to the public, more than 20,000 volunteers around the world tried it out over a period of several months, with no major safety concerns reported among trial volunteers from the US to Argentina, South Africa, Germany, Brazil, and Turkey. Common - but temporary - side effects reported in the trials included pain at the injection site (in the arm), fatigue, and headaches, generally lasting about a day or two post-jab.

The same was generally true of Moderna's new coronavirus vaccine, which was also tested out in more than 15,000 volunteers across the US. 

Both shots were deemed more than 94% effective at preventing symptomatic coronavirus infections, making them critical disease-fighting tools at this stage in the pandemic. The coronavirus is now among the leading causes of death in the US, killing more than 3,000 people across the country every day.  

However, some concerns have been raised about seven people who received the vaccine in trials from Pfizer and Moderna, who developed a temporary form of facial paralysis called Bell's palsy.

What is Bell's palsy, and is it a concern?

The condition involves a sudden weakness of the face, usually on one side. Why this happens isn't well understood, although the paralysis is linked to inflammation of facial nerves.

People with Bell's palsy may have trouble closing one eye, wrinkling their forehead, or pulling up the corner of their mouth to swallow food. Most people make a full recovery in six months or less. 

The FDA has said that it can't rule out with absolute certainty that Pfizer and Moderna's vaccine did not have an impact on these seven cases, and the agency will continue to investigate the issue. But based on the evidence we have, there's no reason to think the vaccine caused the facial paralysis, according to Dr. Nate Jowett, director of the surgical photonics & engineering laboratory at Mass Eye & Ear, and an associate professor of otolaryngology at Harvard Medical School. 

"At this point, there's no evidence to support that these vaccines trigger an increased risk of Bell's palsy, it's really important for the public to understand that," Jowett told Insider. 

The number of cases is small enough to be explained by coincidence

Four people in Pfizer's trial, and three in Moderna's, developed the condition, out of a total of more than 37,000 people in both studies. (At least one unvaccinated person in Moderna's trial also developed Bell's palsy.)

In other words, 99.98% of people who got two doses of a coronavirus vaccine did not develop Bell's palsy, and just 0.02% did. 

That rate is no higher than would be expected among the general population, according to the FDA. 

The number of cases is small enough that they may not be related to the vaccine at all, according to Jowett, given how commonly the condition occurs in the population. 

"The number of Bell's palsy cases that occurred in those massive cohorts is completely within the number you'd expect to happen by chance alone in a regular population without a vaccine or pandemic happening," he said. 

In a typical year, data suggests that for every 100,000 people in the population, 15 to 30 people will develop Bell's palsy. In contrast, out of more than 37,000 vaccine recipients, seven developed Bell's palsy. While Jowett said it's "somewhat unusual" that most of the cases occured in people who received the vaccine, compared to one case in the placebo group, it's not significant enough to suggest a causal link. 

"Those numbers are well within what you'd expect statistically to note by pure random association. You'd expect 5-10 people would develop Bell's palsy by chance during that follow up," Jowett said. 

The FDA has acknowledged that more people who received the coronavirus vaccines developed Bell's palsy than those who got a placebo, and the agency will continue monitoring for more cases, as the vaccine is rolled out to states.

Vaccine expert Paul Offit, who is a member of the FDA's independent advisory board on vaccines, said during a committee meeting on Thursday that he was pleased the agency is going to continue to closely monitor these vaccines going forward, given that there were more paralysis cases in the vaccinated groups than among controls.

Still, he stressed that it is important to not fall victim to "the tyranny of small numbers" and conclude any vaccine-Bell's relationship just yet. 

Bell's palsy is linked to latent viruses like chickenpox

Facial paralysis is linked to viruses generally, but not specifically to the novel coronavirus that causes COVID-19. Instead, research suggests that Bell's palsy can be triggered by certain viruses that are already in our bodies, lying dormant. 

"Our best evidence suggests it is the result of the reactivation of a virus [such as chickenpox or other herpes viruses]," Jowett said. "These are benign viruses most of us pick up as children and we carry them for the rest of our lives."

When we recover from such viral illnesses, they remain in a usually-harmless or latent form in our bodies (including in our nerves). In rare cases, these viruses can reactivate, causing conditions such as shingles. Science doesn't completely understand why this happens, but it may be triggered by stress or immune disruption. 

Bell's palsy can occur when viral reactivation causes inflammation in the nerves of the face, triggering muscle weakness and paralysis. 

It's also been associated with other underlying health conditions, such as diabetes, high blood pressure, and upper respiratory infections, according to the National Institute of Neurological Disorders and Stroke. 

Several COVID-19 vaccine recipients who developed Bell's palsy also reported these associated illnesses, including a 67-year-old woman with diabetes, and a 30-year-old woman who had a respiratory infection a month prior to getting the vaccine. 

Bell's palsy is the most common diagnosis for facial paralysis, but other conditions can have the same symptoms, including Lyme disease and strokes, according to Jowett.

Most patients make a full recovery

Bell's palsy is rarely considered to be a serious illness as patients nearly always recover on their own, without needing treatment. In the vaccine studies, two of the Bell's cases were reported as completely resolved, and many of the other five were resolving, as Pfizer and Moderna submitted their safety data to the FDA. 

"The vast majority of cases are not serious in that they will completely, spontaneously resolve within a few days to a few weeks, with complete return of normal facial function," Jowett said. 

If necessary, steroids and anti-viral medications can be used in severe cases to help improve the odds that patients will return to normal more quickly. 

Infrequently, Bell's palsy can cause longer lasting symptoms. 

"In severe cases, nerve fibers can be damaged and regenerate, but connected to the wrong muscle," Jowett said. "For instance, when a patient starts to smile, their eye may involuntarily close."

These ongoing issues can be treated with physical therapy, medical Botox, and surgery if necessary, he said. 

Experts have debunked the idea that vaccines cause Bell's palsy before

According to Jowett, the theory that vaccines are linked to Bell's palsy is primarily based on one 2004 study of a new flu vaccine. That vaccine was distributed in Switzerland during the 2000-2001 flu season and was linked to a significant increase in cases of Bell's palsy (at least 13 extra cases for every 10,000 vaccine recipients). No extra cases were reported in the US though, because the Swiss-made vaccine was pulled from the market before it got to the states.

However, later evidence found that it was likely the way the vaccine was administered that was the real culprit. The 2000 vaccine was the world's first licensed intranasal flu mist, administered through the nose instead of with a needle in the arm.

In a follow-up study, researchers administered similar strains of the same flu vaccine as a shot into muscle fibers, and found it was not linked to any more cases of facial paralysis. 

"It's possible that proximity to facial nerve fibers somehow induced inflammation in the nerve, which is what triggers Bell's palsy," Jowett said. 

Both Pfizer and Moderna's new mRNA vaccines are injected into people's arm muscles, not administered through the nose.

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