Bell’s Palsy After Covid Vaccination Very Rare, Benefits Of Shots Far Outweigh Risk: Study In Lancet

Bell’s palsy, also known as ‘acute peripheral facial nerve palsy of unknown cause’, commonly manifests with sudden onset of one-sided facial paralysis.

New Delhi: A new study has found that the “beneficial and protective effects” of SARS-CoV-2 vaccines far outweigh the risk of Bell’s palsy — a rare adverse event reported in the clinical trials of mRNA Covid-19 vaccines earlier. 

The findings of the first large-scale population-based study on the association between two Covid-19 vaccines and Bell’s palsy were published in The Lancet Infectious Diseases journal Tuesday.

A Bell’s palsy patient suffers from sudden one-sided facial paralysis. The condition is usually temporary and resolves itself in a few months’ time in most cases, with or without treatment.

Researchers in Hong Kong analysed Bell’s palsy cases linked to CoronaVac (Sinovac Biotech) and BNT162b2 (Pfizer-BioNTech), the two approved Covid-19 vaccines in the territory. 

The study, funded by the Food and Health Bureau of the Government of Hong Kong Special Administrative Region, used official data that included reports of adverse events recorded throughout the territory. Bell’s palsy cases were included if they occurred within 42 days of the first or second dose of the vaccine, within the timeframe of the study, The Lancet said in a statement. 

The study conducted by Eric Yuk Fai Wan, Assistant Professor at the Department of Family Medicine and Primary Care, University of Hong Kong, and his colleagues found a “small increased risk” of Bell’s palsy for people who took CoronaVac. For every 1 lakh people vaccinated with the inactivated Covid vaccine, an additional 4.8 people could develop the condition, the study said. 

The increased risk associated with the mRNA Pfizer-BioNTech vaccine was, however, found to be “non-significant”.

While the current prescribing information for CoronaVac does not list Bell’s palsy as a rare adverse event, approval has been obtained to include information on the potential association based on the findings from the study.

The European Medicines Agency has already reported acute partial facial paralysis as a rare side effect of the Pfizer-BioNTech and mRNA-1273 (Moderna) mRNA vaccines.

The researchers also conducted a “nested case-control study” using an electronic health record database that included 298 Bell’s palsy cases and 1,181 matched controls.

What Is Bell’s Palsy?

Also known as “acute peripheral facial nerve palsy of unknown cause”, Bell’s palsy usually manifests with a sudden onset of one-sided or unilateral facial paralysis. 

In about 70 per cent cases, however, the condition resolves itself within a period of six months without any treatment, according to the Lancet statement. Early treatment “with corticosteroids” increases the chance of recovery to 90 per cent, it added.

Patients with incomplete recovery, however, might have “incomplete eye closure, brow ptosis, and nasal valve collapse”. 

“Our study suggests a small increased risk of Bell’s palsy associated with CoronaVac vaccination. Nevertheless, Bell’s palsy remains a rare, mostly temporary, adverse event,” Professor Ian Chi Kei Wong of the University of Hong Kong, lead author of the study, said in the statement.

“All evidence to date, from multiple studies, shows that the beneficial and protective effects of the inactivated COVID-19 vaccine (CoronaVac) far outweigh any risks.”

mRNA Vaccines And Bell’s Palsy

While the clinical trials of mRNA Covid-19 vaccines have reported a small number of Bell’s palsy cases, analyses of the association have so far thrown up conflicting conclusions. 

The US Federal Drug Administration (FDA) did not consider any clear causal association for the two mRNA vaccines — Pfizer-BioNTech and Moderna — but recommends “ongoing safety surveillance”, which is always required for any new treatment or vaccines to understand the prevalence of rare adverse events.

Only very large population studies, after the initial randomised controlled trials, make this possible, according to the Lancet statement. 

“Ongoing surveillance, through pharmacovigilance studies such as ours are important to calculate with increasing levels of confidence the risks of rare adverse events,” Professor Ian Chi Kei Wong said. 

What The Hong Kong Study Found

The Hong Kong health authorities, between February 23 and May 4, 2021, found 28 clinically confirmed cases of Bell’s palsy identified among the 4,51,939 people who received at least one shot of CoronaVac, which comes to 3.61 cases per 100,000 doses. Among the 537,205 individuals who received at least one dose of the BNT162b2 vaccine, as many as 16 Bell’s palsy cases were identified — equivalent to 2.04 cases per 100,000 doses.

The researchers also checked the background risk of Bell’s palsy in Hong Kong, by studying data from 2010 to 2020, and found around 27 cases per 100,000 people per year — against the global estimates of 15-30 cases per 100,000 people, per year. 

The nested case-control study conducted by them found that CoronaVac was linked to 2.4 times increased risk of Bell’s palsy, while BNT162b2 was not associated with a “significantly increased risk”.

They concluded that an additional 4.8 people for every 100,000 people who got CoronaVac could develop Bell’s palsy. The increased risk for BNT162b2 was found to be an additional 2 cases per 100,000 people vaccinated. This finding, however, could be attributed to “underpower” in the study, the authors noted and said more studies with a sufficient sample size were needed to evaluate the association between BNT162b2 and Bell’s palsy.

The authors said the mechanism by which vaccination can — “in very rare instances” — lead to Bell’s palsy remains unclear. 

Other studies earlier have identified rare cases of Bell’s palsy after administration of other inactivated vaccines, such as that for influenza. 

The authors said their study is limited to patients with a new diagnosis of Bell’s palsy in Hong Kong, and hence further studies including patients in other regions, and those with a history of Bell’s palsy, should be done to confirm their findings. They said further studies are also needed to understand if the risk varies according to gender or age. 

Quoting Professor Nicola Cirillo from the University of Melbourne, Australia, and Dr Richard Doan, University of Toronto, Canada, (who were not involved in the study), the statement said: “From a clinical, patient-oriented perspective, none of the studies published so far provide definitive evidence to inform the choice of a specific vaccine in individuals worldwide with a history of Bell’s palsy. However, the data published by Wan and colleagues do offer valuable information for a rational and informed choice of COVID-19 vaccines for patients in Hong Kong, and for those in countries where both BNT162b2 and CoronaVac are available.”

They added: “While waiting for conclusive evidence on vaccine-associated facial paralysis, one certainty remains: the benefit of getting vaccinated outweighs any possible risk.”