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VERIFY: What do we know about the connection between the Pfizer vaccine and Bell's Palsy?

Four participants in the Pfizer trials developed Bell's palsy. It's spurred a lot of conversation online, but experts can't say the vaccine caused it.

As the rollout of the Pfizer COVID-19 vaccine begins, how our bodies will react to the shot is at the top of mind for most Americans. 

While we know that it has a 95% efficacy for preventing severe illness caused by COVID-19, reports of side effects have some Americans worried.

QUESTION: 

What do we know about the connection between the Pfizer vaccine and Bell’s palsy?

ANSWER:

Four Pfizer vaccine trial participants out of 43,000 were diagnosed with Bell's palsy. That rate is about on par with the yearly rates of Bell's palsy cases in the U.S. every year, so they can't say whether the vaccine caused Bell's palsy.

SOURCES:

  • Pfizer
  • The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) briefing
  • Dr. Arnold Monto, Acting chair of VRBPAC 
  • Dr. Kawsar Talaat, vaccine expert and Assistant Professor at John Hopkins University

PROCESS:

With vaccine distribution rolling out, one viewer sent us a link to an Instagram post that stated four Pfizer vaccine participants developed Bell's palsy afterward. 

So we decided to take a look. The image shared on the Instagram post was not actually of the four participants who developed Bell's palsy — that wouldn't be shared. The image can instead be traced back to this health education website.

The Mayo Clinic describes Bell's palsy as a sudden weakness in your facial muscles, often temporary and significantly improves over weeks. "The weakness makes half of your face appear to droop. Your smile is one-sided, and your eye on that side resists closing."

In the Pfizer vaccine trials, there were four incidences of participants who developed Bell's palsy. But the company, and many experts. explain that the rate of occurrence in the trial is about on par with what we see in the U.S. every year.

Pfizer provided this statement:

“The observed frequency of reported Bell’s palsy in the vaccine group is consistent with the expected background rate in the general population, and there is no clear basis upon which to conclude a causal relationship at this time. Pfizer and BioNTech together with FDA will continue to monitor for cases of Bell’s palsy with deployment of the vaccine into larger populations.”

RELATED: Verify: No, the coronavirus vaccines will not alter your DNA

The Verify team did the math ourselves: 

  • There were four cases developed out of 43,000 trial participants; that's a rate of 9.3 per 100,000 people. 
  • All cases were found in the group of 21,720 participants who received the vaccine, which gives a rate of 18.4 in 100,000
  • In a normal year in the U.S., experts confirmed the diagnosis rate can range from 12 to 25 per 100,000 people.

Dr. Arnold Monto is the acting chair of the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC). He told us that while there were more cases of Bell’s palsy in the vaccine group than in the placebo group, that it was quote “not out of line with the routine occurrence of Bell’s palsy in the population, so we cannot say the vaccine caused it.”

The Food and Drug Administration said essentially the same in a briefing in early December: “Bell’s palsy was reported by four vaccine participants...This observed frequency of reported Bell’s palsy is consistent with the expected background rate in the general population."

“In general Bell's palsy is a response of your body to viral infection, So different viruses can trigger it," Dr. Kawsar Talaat tells us. "With the exception of one vaccine that was never sold in the United States and taken off the market very, very quickly, there's never been any vaccines that have been shown to cause Bell's palsy…So I think that while Bell's palsy can happen in response to viruses, it's unlikely that it's going to happen in response to the COVID vaccine study.”

So we can Verify that right now, our experts don't believe that the Pfizer COVID-19 vaccine causes Bell's palsy.