Fact check: Bell's palsy among COVID-19 trial participants likely unrelated to Pfizer vaccine

Editor's note: The image source for the first Facebook post, previously unknown, has been determined and included in this article. 

The claim: FourPfizer COVID-19 vaccine trial participants developed facial paralysis

The U.S. Food and Drug Administration authorized emergency use of the Pfizer-BioNTech COVID-19 vaccine on Dec. 11, and deployment of the vaccine began Dec. 14. While the vaccine heralds an end to the nearly yearlong pandemic, some on social media are raising concerns. 

"Four Pfizer vaccine volunteers (for COVID-19) develop Bell's palsy," claims a Dec. 12 Facebook post.

An explanation of Bell's palsy is later offered ("a condition that causes a weakness or paralysis of the muscles in the face"), and the post claims the side effect is being considered a " 'non-serious' reaction" despite the worrisome image included of three individuals with lopsided facial expressions.

Readers are encouraged to confirm the finding for themselves by following a link to an "FDA.gov review" provided at the bottom.

Similar posts elsewhere on Facebook echo the findings but instead share a screenshot of a Daily Mail headline juxtaposed with an image of three different individuals also afflicted with some sort of facial palsy.

USA TODAY has reached out to both Facebook users who shared the posts. 

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Bell's palsy likely unrelated to vaccine

On Dec. 10, the FDA's Center for Biologics Evaluation and Research held the 162nd meeting of the Vaccines and Related Biological Products Advisory Committee to discuss the emergency use authorization of the Pfizer-BioNTech COVID-19 vaccine. 

A 53-page briefing noted that there had been four cases of Bell's palsy among the vaccinated group and none among the placebo group. Symptoms occurred at different time points: For one participant, the condition occurred three days post-vaccination but resolved within three days; for the other three, symptoms appeared at nine, 37 and 48 days following vaccination and lasted for about 10, 15 and 21 days, respectively.

While developing a temporary neuromuscular condition during a vaccine trial may sound concerning, it is best to put this finding into perspective. The annual incidence rate for Bell's palsy within the general population is around 23 cases per 100,000 people or 15-20 per 100,000 people, according to some population studies. Translating that to the trial's four cases out of 38,000 trial participants, it computes to 11 cases per 100,000 people.  

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Thus, because the finding was "consistent with the expected background rate in the general population," the trial ruled there was "no clear basis upon which to conclude a causal relationship" between the vaccine and the occurrence of Bell's palsy.

The briefing did acknowledge the FDA will continue to monitor for any new cases or reports of Bell's palsy once the vaccine is deployed into larger populations. 

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What causes Bell's palsy? 

It is unclear why the four participants developed Bell's palsy and little is known about what exactly causes the condition. One prevailing theory is that herpes simplex virus may be the culprit.

HSV comes in two types, depending on the route of transmission — oral for HSV-1 and genital, or sexually transmitted, for HSV-2. It is HSV-1 that may be hiding away deep within facial nerves in a deactivated form, activating only when its human host comes under stress. Viral activation leads to infection and damage to the local facial nerves, resulting in the characteristic facial drooping or muscle weakness.  

According to the Centers for Disease Control and Prevention, nearly 48% of the U.S. population has HSV-1 per 2015-2016 data. This percentage could be higher since an individual infected with the virus may never show symptoms. 

Although herpes is a lifelong infection, Bell's palsy is completely treatable with anti-inflammatory drugs like corticosteroids and, in some severe cases, antiviral therapy as well. Approximately 80% to 90% of patients recover fully within six weeks to three months. Recurrence for Bell's palsy is estimated at 5% to 15%. 

There are certain conditions that can put an individual at a higher risk for developing Bell's palsy, such as pregnancy, hypertension or diabetes.

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Images not associated with COVID-19 vaccine trial

The first image of three individuals against a bright blue background is not from the Pfizer COVID-19 vaccine trial, but from a 2019 study associated with Massachusetts Eye and Ear Infirmary in Boston. 

"The images being shared of the people who developed Bell's Palsy from the vaccine are taken from a facial paralysis paper written by our doctors and are NOT the patients related to the Pfizer vaccine trials," stated MEEI's Facial Nerve Center on Twitter.  

One individual from the second image alongside the Daily Mail headline can be found in an article on tetanus; another can be found in an American Academy of Ophthalmology article from May 2008 and is clearly characterized as having a "left facial palsy."  

USA TODAY has reached out to both Pfizer and the FDA to verify the origin of the second photo.

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Our rating: Missing context

We rate this claim MISSING CONTEXT, because without additional context it might be misleading. According to a Dec. 10 briefing document from the U.S. Food and Drug Administration, four volunteers from Pfizer-BioNTech's COVID-19 vaccine trial did develop a type of facial paralysis/weakness called Bell's palsy. However, this was not considered significant, given it was comparable to incidence of Bell's palsy in the general population. It is also important to note a correlation between two events, phenomena or variables does not imply causation.

The image from the first Facebook post was taken from a 2019 study out of Boston's Massachusetts Eye and Ear Infirmary examining facial palsy. Individuals from the second photo do not appear to be the actual trial participants or have facial palsy with exception of one. 

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