One adverse event common to clinical trials for currently authorized COVID-19 vaccines is Bell’s palsy, an asymmetrical weakness or paralysis of the face that is often temporary.
Two vaccine recipients in the Johnson & Johnson Phase 3 clinical trial developed Bell’s palsy, as did two people in the placebo group. Another patient developed facial swelling and “droopiness” without facial asymmetry. A clinical trial investigator concluded that this event was unrelated to the vaccine.
Three vaccine recipients in the Moderna Phase 3 clinical trial developed Bell’s palsy, as did one in the placebo group. In the corresponding Pfizer-BioNTech study, four vaccine recipients developed Bell’s palsy, but no participants in the placebo group did.
The three Phase clinical trials involved some 30,000 to 40,000 volunteers.
The numerical imbalance between the rates in vaccine and placebo in the Pfizer and Moderna trials prompted FDA and CDC to monitor vaccine recipients for Bell’s palsy.
But the FDA has not concluded that those vaccines cause the condition.
CDC has stated that more data are needed to “further assess any possible causal association” and encourages people with a history of Bell’s palsy to receive mRNA COVID-19 vaccines “unless they have a contraindication to vaccination.”
An article recently published in The Lancet analyzed the combined Phase 3 data from Pfizer and Moderna and concluded that the rate of Bell’s palsy across the two trials was between 3.5 and 7 times higher than the expected rate in the general population. “This finding signals a potential safety phenomenon and suggests inaccurate reporting of basic epidemiological context to the public,” the paper argues.
The article goes on to call for adequate surveillance of vaccine recipients for Bell’s palsy, but also stresses that “ the available coronavirus mRNA vaccines offer a substantial net benefit to public health.”
One hypothesis is that many Bell’s palsy cases result from viruses such as herpes simplex and herpes zoster. Pregnancy and diabetes increase the risk of developing the form of facial paralysis.
Researchers also have evaluated the risk of Bell’s palsy from influenza vaccines.
An inactivated intranasal influenza vaccine that debuted in Switzerland in the early 2000s was pulled off the market after researchers discovered it to have a risk of causing Bell’s palsy.
A monovalent pandemic H1N1 influenza vaccine also appeared to be associated with a higher incidence of Bell’s palsy, according to the Lancet.