COVID-19 vaccine trials report cases of brief facial paralysis. That's not as scary as it sounds.

Americans are increasingly concerned about vaccine safety after four people in Pfizer-BioNTech trials and three people in the Moderna trials developed Bell’s palsy, a condition that causes temporary weakness or paralysis of the facial muscles.

While it may sound scary, experts say Bell’s palsy is more common and less severe than people think.

Bell’s palsy, also known as peripheral facial nerve palsy, can occur at any age, according to the Mayo Clinic. The exact causes are unknown, but it’s believed to be the result of swelling and inflammation of the nerve that controls the muscles on one side of the face, or a reaction after a viral infection.

Dr. Anthony Geraci, Northwell Health’s Director of Neuromuscular Medicine in Great Neck, New York, says at least two Bell’s palsy patients visit his office a month, and they always recover within several weeks.

“Ninety percent, if not more, of patients who have Bell’s palsy experience a mild, transient weakness of the side of the face which is completely resolved within three months, the majority within a month and a half,” he said. “It’s a relatively benign condition.”

According to the Mayo Clinic, symptoms of Bell’s palsy may include rapid onset of mild weakness to total paralysis on one side of the face, facial droop, pain around the jaw or behind the ear, increased sensitivity to sound, headache, a loss of taste and changes in the amount of tears and saliva produced.

But Geraci says most of his patients experience mild to moderate symptoms. That could include numbness or tingling to the tongue, or maybe an off-kilter smile or less blinking in one eye than the other.  

He says symptoms can be so subtle most people wouldn’t notice someone has Bell’s palsy to look at them.

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“I challenge somebody to notice that someone is blinking less in one eye than the other,” he said.

The Mayo Clinic says common causes of Bell’s palsy include, herpes, chickenpox and shingles, respiratory illness, mumps or rubella or even the flu. Geraci said most patients are treated with antivirals and make a full recovery.

Twenty-five to 35 patients per 100,000 population  get Bell’s palsy in the U.S. every year, the National Organization for Rare Disorders reported. About 40,000 Americans a year are diagnosed with it.

Geraci notes that is more frequent than what was recorded in the COVID-19 vaccine trial.

“Four persons out of almost 40,000 is even less than what we would expect to see when we take 40,000 people from the street and watch them for three months” independent of a vaccine, he said.

He also emphasized that there were not enough cases to determine whether they were caused by the vaccine or happened coincidentally. 

Cases of severe or permanent Bell's palsy are extremely rare, Geraci added. In his more than 20-year career, he has seen fewer than than five cases. 

He said it’s important the public understands Bell’s palsy is just a "bogeyman side effect” and shouldn’t prevent someone from getting the COVID-19 vaccine.  

“It’s a cautionary tale that should not mitigate the larger good that both individuals and society are going to derive from all of these vaccines,” Geraci said.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT. 

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.