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People with COVID-19 were more likely to develop Bell's palsy (peripheral facial nerve palsy) than people who were vaccinated against the virus, an analysis of medical records showed.

Matching COVID-19 patients with vaccinated individuals showed that people with COVID-19 were nearly seven times more likely to have a diagnosis of Bell's palsy than those who were vaccinated (OR 6.8, P<0.001), reported Akina Tamaki, MD, of University Hospitals Cleveland Medical Center, and co-authors in a research letter in .

And in a , Asaf Shemer, MD, of Shamir Medical Center in Be'er Ya'akov, Israel, and colleagues found no association between recent vaccination with the Pfizer-BioNTech COVID-19 vaccine and risk of facial nerve palsy.

When Pfizer-BioNTech and Moderna revealed adverse events in their trials, concerns about Bell's palsy and the vaccines grew, observed C. W. David Chang, MD, of the University of Missouri in Columbia, writing in an accompanying the two papers.

"Epidemiologically, linking the vaccine with an adverse event requires accurate estimation of event incidence in association with the vaccine, comparison with a nonvaccinated group, and understanding of the background incidence," he explained.

Historical background rates for safety surveillance offer some context, but come with caveats, Chang added: Many publications cite an incidence of 11.0 to 51.9 per 100,000 person-years, but these rates can vary widely. "Further confounding background rates, the COVID-19 pandemic itself has been theorized to affect the incidence of Bell palsy, with mixed findings," he noted.

Tamaki and co-authors searched a large database of records from 41 healthcare organizations from Jan. 1 to Dec. 31, 2020, to determine the rates of Bell's palsy in patients with a COVID-19 diagnosis. Of 348,088 people with COVID-19, 284 had a Bell's palsy diagnosis within 8 weeks of COVID diagnosis, including 153 people with new-onset Bell's palsy.

"The authors translate this to an 8-week incidence of 82 per 100,000 patients with COVID-19," Chang said. "However, if using a crude analysis and assuming a pre-pandemic rate of 40 per 100,000 person-years and no seasonality, Bell's palsy would be expected to naturally occur in only 21 of 348,088 patients during an 8-week period."

A comparison of patients with 63,551 matched individuals who were vaccinated from Jan. 1 to March 31, 2021, showed that the incidence of Bell's palsy was lower among people who received COVID-19 vaccines.

In the second paper, Shemer and colleagues evaluated the COVID vaccination and facial nerve palsy risk in a case-control study. Israel is a leading country in vaccination rates per capita, exclusively using the Pfizer-BioNTech vaccine. All residents are part of the national digital health registry system.

From Jan. 1 to Feb. 28, 2021, a total of 37 people were admitted to the emergency department of a tertiary referral center in central Israel. Of these, 21 people (56.8%) had received the vaccine. The researchers compared these people with a group of 74 matched controls and found no difference in vaccination rates (59.5%; adjusted OR 0.84, 95% CI 0.37-1.90, P=0.67).

An analysis of the number of patients with acute-onset facial nerve palsy during January and February in the preceding 5 years showed that the volume was about the same, with an average of 26.8 cases from 2015 to 2020. This figure may have been biased by unmeasured factors such as referral patterns, Shemer and co-authors noted.

"What other real-world data can provide further input? The , which is maintained by the Centers for Disease Control and Prevention, monitors prespecified potential safety signals at nine participating health care organizations using data from all health care encounters," Chang wrote.

As of Feb. 13, 2021, data from 629,523 vaccinated individuals were available, showing 21 cases of Bell's palsy in vaccinated individuals. "This finding is comparable to the 20.3 adjusted expected events among the unvaccinated comparators, thus indicating no increased risk," Chang noted.

Additional sources of real-world data come from voluntary patient safety reporting databases, which carry the potential for underreporting, he pointed out. As of May 15, 2021, the (VAERS) showed 1,743 events of Bell's palsy or facial paralysis after about approximately 270 million COVID-19 vaccine doses among 156 million individuals.

The mRNA COVID-19 vaccines also showed no higher safety signal for facial paralysis than other vaccines in VigiBase, the World Health Organization pharmacovigilance database, earlier this year.

Underreporting may be a factor in both JAMA Otolaryngology-Head & Neck Surgery studies, Chang noted, explaining that adverse effects of COVID vaccines were studied for only a short period; some patients would not have had 8 weeks of observation after vaccination.

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