The beneficial effects of COVID-19 vaccines far outweigh the risk of facial paralysis on one side of the face known as Bell's Palsy, confirms a large-scale population-based study published in The Lancet Infectious Diseases journal.
The researchers from The University of Hong Kong found 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, the condition resolves itself within six months without treatment and the chance of recovery is even higher if patients receive early treatment with corticosteroids, they said.
"Our study suggests a small increased risk of Bell's palsy associated with CoronaVac vaccination," said study lead author Professor Ian Chi Kei Wong from The University of Hong Kong.
"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," Wong said.
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.
In the US, the Federal Drug Administration (FDA) did not consider there to be a clear causal association for the two mRNA vaccines by Pfizer-BioNTech and Moderna but recommends ongoing surveillance.
However, acute partial facial paralysis is reported as a rare side effect of both the vaccines by the European Medicines Agency.
Current prescribing information for CoronaVac does not list Bell's palsy as a rare adverse event.
However, based on the findings from the study, approval has been obtained to include information on the potential association, the researchers said.
The study analysed cases of Bell's palsy related to the two approved vaccines in Hong Kong -- CoronaVac and BNT162b2 (Pfizer-BioNTech).
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.
Between February 23, 2021 and May 4, 2021, 28 clinically confirmed cases of Bell's palsy were identified among the 451,939 individuals who received at least one dose of CoronaVac and 16 cases were identified among the 537,205 individuals who received at least a first dose of BNT162b2.
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, according to the researchers.
The study found that receiving CoronaVac was associated with 2.4 times increased risk of Bell's palsy whereas receiving BNT162b2 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 BNT162b2, the increased risk was equivalent to an additional 2 cases per 100,000 people vaccinated, they said.
Further studies with a sufficient sample size are needed to evaluate the association between Bell's palsy and BNT162b2.
The authors noted 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.
Other studies have identified rare cases of Bell's palsy after other inactivated vaccines, such as influenza, they added.
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