As the Pfizer COVID-19 vaccine has been approved for emergency use authorization by the FDA, it was revealed four trial participants in the United States who received the vaccine developed Bell’s palsy.
The U.S. government has said it will continue to monitor for Bell’s palsy, which often causes partial facial paralysis, although the vaccine does not appear to cause the condition.
On Friday, Dr. Sara Oliver, an Epidemic Intelligence Service officer with the Centers for Disease Control and Prevention’s Division of Viral Diseases, said there is “no known or expected causal relationship between the vaccine and Bell’s palsy,” according to CNBC.
“Post authorization safety and effectiveness studies will be critical as well,” Oliver added. “Specifically, surveillance for Bell’s palsy could help determine any possible causal relationship.”
According to the Mayo Clinic, Bell’s palsy can lead to a sudden weakness in facial muscles and in most cases is temporary. The weakness leads to one side of the face to droop.
While it can affect people of any age, its exact cause is unknown.
“It's believed to be the result of swelling and inflammation of the nerve that controls the muscles on one side of your face,” reads a description on the Mayo Clinic’s website. “Or it might be a reaction that occurs after a viral infection.”
Jason D. Hinman, MD, PhD, assistant professor of neurology at the David Geffen School of Medicine at UCLA, said the four cases of Bell’s palsy from the COVID vaccine trial appeared to be in line with the rate in the general population.
"The normal incidence of Bell's palsy is roughly 20 people out of 100,000,” Hinman told Health. “The Pfizer study examined 38,000 patients, so four cases would be within the normal observed incidence of Bell's palsy."
Pfizer said it would begin shipping its COVID-19 vaccine on Sunday after the FDA authorized the vaccine for emergency use.
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