Benefits of Covid-19 vaccines outweigh very rare risk of Bell’s palsy – study

The benefits of coronavirus vaccines far outweigh a very rare risk of Bell’s palsy, a study suggests.

Bell’s palsy is the sudden onset of one-sided facial paralysis, and in the majority of cases (70%), the condition resolves itself within six months without treatment.

The chance of recovery is even higher (90%) if patients receive early treatment with corticosteroids.

Research suggests a small number of cases have been reported in clinical trials of mRNA Covid-19 vaccines, but analyses of the association have come to conflicting conclusions.

In the US, the Federal Drug Administration (FDA) did not consider there to be a clear causal association for the two mRNA vaccines – the Pfizer/BioNTech (BNT162b2) and Moderna (mRNA-1273) jabs.

Acute partial facial paralysis has been reported by the European Medicines Agency as a rare side effect of both vaccines, which are being used in the UK.

While current prescribing information for China’s CoronaVac (an inactivated vaccine) jab – which is not being used in the UK – does not list Bell’s palsy as a rare adverse event, based on the findings from the study, approval has been obtained to include information on the potential association.

In the new research, published in The Lancet Infectious Diseases journal, researchers analysed cases of the condition related to the two approved vaccines in Hong Kong – CoronaVac and the Pfizer jab.

Bell’s palsy cases were included in the analysis if they occurred within 42 days of a first or second vaccine dose, within the timeframe of the study.

Researchers also conducted a case-control study using territory-wide electronic health records database including 298 Bell’s palsy cases and 1,181 matched controls.

Between February 23 and May 4 this year, 28 clinically confirmed cases of Bell’s palsy were identified among the 451,939 people who received at least a first dose of CoronaVac.

Sixteen cases were identified among the 537,205 individuals who received at least a first dose of the Pfizer vaccine.

Experts analysed data from 2010-20, and estimated the background risk of Bell’s palsy in Hong Kong – around 27 cases per 100,000 people per year.

Global estimates range from 15 to 30 cases.

The nested case-control study found that receiving CoronaVac was associated with 2.4 times increased risk of Bell’s palsy, whereas the Pfizer jab was not associated with a significantly increased risk.

The researchers concluded that for every 100,000 people vaccinated with CoronaVac, an additional 4.8 people may develop Bell’s palsy.

For the Pfizer/BioNTech jab, the increased risk was equivalent to an additional two cases per 100,000 people, which may be attributed to underpower in the current study.

Further studies with a sufficient sample size are needed to evaluate the association between Bell’s palsy and the Pfizer vaccine, researchers said.

Lead author Professor Ian Chi Kei Wong, from the University of Hong Kong, said: “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.

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

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

The scientists could not conclude a causal relationship between Bell’s palsy and vaccination in any individual cases from this study, and the mechanism by which vaccination can, in very rare instances, lead to Bell’s palsy remains unclear.

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

The study was limited to patients with a new diagnosis of Bell’s palsy in Hong Kong, so further studies including patients with a history of Bell’s palsy and patients in other regions should be done to confirm the findings.

Further analyses are also needed to understand whether the risk varies by sex or age, the experts said.