It’s important to understand that we can’t even be certain from this case report that this patient’s Bell’s palsy episodes were caused by the vaccine. That is a possibility, given that both episodes happened quite soon after a vaccine dose – but Bell’s palsy isn’t all that rare a condition and it might be a very unfortunate coincidence that the patient had two episodes at those times. The authors of the case report do make it explicit that “a causal relationship cannot be established.” They also point out that, although there have been a very small number of reports of Bell’s palsy episodes after vaccination with an mRNA vaccine (Pfizer/BioNTech or Moderna), this is the first report that they found in the medical literature of an episode after both Pfizer vaccine doses.

I think that a key point is that, even if the Bell’s palsy in this one patient was caused by the vaccine, a single case report can’t tell you anything about how likely Bell’s palsy might be after vaccination. The fact that the authors of the report couldn’t find many reports of other cases of Bell’s palsy after vaccination, and no others after each of two Pfizer doses, does make it seem that this is, at worst, an extremely rare adverse effect of the vaccine, if it’s a vaccine effect at all. Bell’s palsy isn’t common, but nor is it extremely uncommon. It’s reported that there are between 20 and 30 cases annually for every 100,000 people, which would mean there are between about 13,500 and 20,500 cases in the UK each year. According to bellspalsy.org.uk, the condition “will affect one in 60 UK citizens at some point during their lifetime.” So you would expect some cases of Bell’s palsy to develop soon after vaccination just by coincidence. My feeling is that, even if there does turn out to be a causal link with vaccination (and that’s certainly not known yet), it’s likely to happen so rarely that this doesn’t affect the balance between the risk of possible vaccine side effects and the risk of bad consequences if you’re not vaccinated and catch Covid-19.

MHRA are keeping an eye on this. They write in their most recent weekly summary of yellow card (possible adverse effect) reporting on the coronavirus vaccines, published last Friday (16 July) ±, “The MHRA continues to review cases reporting Bell’s Palsy and to analyse case reports against the number expected to occur by chance in the absence of vaccination (the ‘natural rate’). The number of reports of facial paralysis received so far is similar to the expected natural rate and does not currently suggest an increased risk following the vaccines. We will continue to monitor these events, including through evaluation of electronic healthcare record data."

± https://www.gov.uk/government/publications/coronavirus-covid-19-vaccine-adverse-reactions/coronavirus-vaccine-summary-of-yellow-card-reporting

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