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People who received a COVID-19 vaccine were more likely to develop Bell's palsy than those who weren't vaccinated, but the risk of Bell's palsy was higher among people with SARS-CoV-2 infection, a systematic review and meta-analysis showed.

Pooled data from vaccine clinical trials showed the odds of developing Bell's palsy were higher in 77,525 SARS-CoV-2 vaccine recipients compared with people who received placebo (OR 3.00, 95% CI 1.10-8.18), reported Amir Kheradmand, MD, a neurologist at Johns Hopkins University School of Medicine in Baltimore, and co-authors in .

Compared with vaccination, however, SARS-CoV-2 infection tripled the risk of developing Bell's palsy (relative risk 3.23, 95% CI 1.57-6.62). The occurrence of Bell's palsy did not vary among different vaccines.

"Bell's palsy has been reported as an adverse event following the SARS-CoV-2 vaccination, but neither a causative relationship nor a higher prevalence than in the general population has been established," said study coauthor Ali Rafati, MD, MPH, of the Iran University of Medical Sciences in Tehran. "This is the first meta-analysis that addressed whether SARS-CoV-2 vaccination and infection are associated with Bell's palsy."

"These findings show that the benefits of vaccinating against SARS-CoV-2 enormously outweigh the potential risk of developing Bell's palsy," Rafati told 麻豆传媒. "Considering Bell's palsy as the adverse event, SARS-CoV-2 infection is associated with a 3.23-fold increase in Bell's palsy risk compared to vaccination."

Bell's palsy is a form of temporary paralysis or weakness on one side of the face; symptoms appear suddenly over a few days and usually start to improve after a few weeks.

There's precedence for vaccines being associated with an elevated risk of Bell's palsy, noted Nate Jowett, MD, PhD, of Massachusetts Eye and Ear and Harvard Medical School in Boston, who wasn't involved with the study. "In 2004, an inactivated intranasal influenza vaccine approved for use in Switzerland was shown to significantly , with a relative risk estimate at 19 times the risk in controls within 1 to 91 days after vaccination, and was discontinued," Jowett wrote in an email to 麻豆传媒.

When mRNA vaccines first received emergency approval, there was some concern they might trigger a slightly higher risk of Bell's palsy, Jowett said.

He cited data at 5-6 months follow-up showing small and nonsignificant imbalances in the rate of Bell's palsy cases between treatment and control groups in both the original Moderna (8 cases in vaccine group, 3 cases in control group) and Pfizer (4 cases in vaccine group, 0 cases in control group) mRNA vaccine randomized controlled trials.

Moreover, the FDA Center for Biologics Evaluation and Research Office of Biostatistics and Pharmacovigilance, in its of COVID-19 mRNA vaccine boosters on August 31, 2022, noted a small but significant risk for Bell's palsy among the Medicare population with prior COVID-19 infection (rate ratio of 1.11, 95% CI 1.03-1.19), Jowett added.

However, no incidents of Bell's palsy have been reported in children ages 6 months through 17 years in Moderna and Pfizer mRNA vaccine trials to date, he said.

Kheradmand and coauthors evaluated studies about Bell's palsy and COVID vaccines or infection from December 2019 to August 15, 2022. They incorporated 17 studies into their quantitative analysis, including four phase III randomized clinical trials of vaccines -- one each for Pfizer/BioNTech, Moderna, Janssen, and Oxford/AstraZeneca -- that reported Bell's palsy as an adverse event.

Pooled data from observational studies comparing Bell's palsy in 13.5 million mRNA vaccine recipients and a matched group of unvaccinated individuals showed no significant increase in Bell's palsy (OR 0.70, 95% CI 0.42-1.16). No significant difference emerged in Bell's palsy risk among 23 million first-dose recipients of the Pfizer/BioNTech vaccine compared with 23 million first-dose recipients of the Oxford/AstraZeneca vaccine (OR 0.97, 95% CI 0.82-1.15).

The study had several limitations, Kheradmand and colleagues acknowledged. It relied on previously published data and no individual patient-level data were available. Only a small number of studies, mostly case reports, reported data on Bell's palsy treatments and outcomes.

The researchers also could not examine whether study participants had Bell's palsy risk factors like diabetes, obesity, hypertension, upper respiratory tract disease, or pregnancy.

"This study shows evidence for the association between SARS-CoV-2 and Bell's palsy, however, this finding does not equate to causality," Rafati noted. "Further research is required to verify this association and investigate possible mechanisms."

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