Updated: August 18, 2021 7:26:32 am
The first large-scale population-based study on the association between the SARS-CoV-2 vaccines and Bell’s palsy confirms that the beneficial and protective effects of the vaccines far outweigh the risk of this rare adverse event.
The study, published online on Tuesday in the Lancet Infectious Diseases journal, finds that for every 100,000 people vaccinated with inactivated vaccine, CoronaVac, an additional 4.8 people may develop the condition.
Bell’s palsy is the sudden onset of one-sided facial paralysis. In the majority of cases (70%), the condition resolves itself within six months without treatment and the chance of recovery is even higher (90%) if patients receive early treatment with corticosteroids.
A small number of cases of Bell’s palsy have been reported in clinical trials of mRNA Covid-19 vaccines, but so far, analyses of the association have come to conflicting conclusions, the Lancet study has said.
In the USA, the Federal Drug Administration (FDA) did not consider there to be a clear causal association for the two mRNA vaccines BNT162b2 (Pfizer-BioNTech) and the mRNA-1273 (Moderna) vaccines but recommends ongoing surveillance.
Acute partial facial paralysis is reported as a rare side effect of both vaccines by the European Medicines Agency. Current prescribing information for CoronaVac (an inactivated vaccine) does not list Bell’s palsy as a rare adverse event, but based on the findings from the study, approval has been obtained to include information on the potential association.
In this study, researchers analysed cases of Bell’s palsy related to the two approved vaccines in Hong Kong – CoronaVac and BNT162b2. The study used data from the Hong Kong drug regulatory authority pharmacovigilance system, which includes reports of adverse events logged by health professionals throughout the territory. Cases of Bell’s palsy were included in the analysis if they occurred within 42 days of the first or second vaccine dose, within the timeframe of the study. They also conducted a nested case-control study using territory wide electronic health record database including 298 Bell’s palsy cases and 1,181 matched controls.
Between February 23, 2021 and May 4, 2021, 28 clinically confirmed cases of Bell’s palsy were identified among the 4,51,939 individuals who received at least a first dose of CoronaVac (equivalent to 3.61 cases per 100,000 doses administered) and 16 cases were identified among the 537,205 individuals who received at least a first dose of BNT162b2 (equivalent to 2.04 cases per 100,000 doses administered).
By analysing data from 2010-2020, the researchers estimated the background risk of Bell’s palsy in Hong Kong – around 27 cases per 100,000 people, per year. Global estimates range from 15-30 cases per 100,000 people, per year.
“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,” says lead author Professor Ian Chi Kei Wong, University of Hong Kong.
The authors note that they cannot conclude a causal relationship between Bell’s palsy and vaccination in any individual cases from this study, and that the mechanism by which vaccination can – in very rare instances – lead to Bell’s palsy remains unclear.
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