A man developed Bell's palsy after receiving both doses of the Pfizer-BioNTech coronavirus vaccine, a case report has revealed.
The unnamed man, 61, experienced weakness and a lack of movement on the right side of his face five hours after being injected with the first jab on 18 January.
Six weeks later, a more severe episode occurred on his left side two days after the second vaccine – causing the man to dribble and struggle to swallow. He is said to be almost back to normal after a short course of steroids.
Bell's palsy is thought to occur when a facial nerve becomes inflamed, often due to a viral infection. This results in weakness or a lack of movement on one side.
Four cases were reported in the trial that led to the Pfizer-BioNTech vaccine being approved. In 2004, a flu jab was discontinued after being linked to the side effect.
Bell's palsy generally improves within nine months, with seven in 10 cases making a complete recovery with or without treatment. Weakness persists in three in 10 incidences, while two in 10 endure "a more serious long-term problem", like difficulty speaking, eating or drinking.
Writing in BMJ Case Reports, medics from the Royal Surrey County Hospital NHS Foundation Trust in Guildford state the incidence "strongly suggests a link" between the Pfizer-BioNTech vaccine and Bell's palsy.
Nevertheless, the benefits of being vaccinated are thought to far outweigh any risk in the vast majority of people.
This is the first known case of Bell's palsy occurring after both jabs of any coronavirus vaccine that has a two-dose regimen.
Episodes had previously been reported after one of the jabs in both clinical trials and real-life settings.
In the Pfizer-BioNTech vaccine's final trial, four Bell's palsy cases occurred among the volunteers who received the jab – versus none in the placebo group – out of 38,000 volunteers.
"This was reported as no higher than the expected incidence in the general population and a causal relationship was therefore not established," wrote the medics.
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"Facial drooping" is said to affect one in 1,000 people after the Pfizer-BioNTech jab. From 9 December, 2020, to 5 April, 2021, 291 facial paralysis cases "associated with the vaccine" were reported in the UK.
The Medicines & Healthcare products Regulatory Agency (MHRA) has said "this number is similar to the expected rate in the population", but it is monitoring the situation.
In the Moderna coronavirus vaccine trial – a jab that is based on the same technology as the Pfizer-BioNTech injection – three Bell's palsy cases occurred in the vaccine arm and one in the placebo group, out of more than 30,400 volunteers.
The side effect similarly arose in the University of Oxford-AstraZeneca coronavirus vaccine study – affecting three volunteers in both the jab and placebo groups out of more than 23,000 participants.
The unnamed man had never experienced Bell's palsy before the vaccines but had several risk factors for the facial weakness, including diabetes and high blood pressure.
The day after he developed the side effect, the man went to his local A&E department, where medics found no serious cause for concern.
He was diagnosed with Bell's palsy and discharged with a short course of steroids. The facial weakness "completely resolved" and the man was booked in for his second vaccine.
Two days after that jab, however, a "more severe" Bell's palsy case occurred on his left side.
The man was prescribed the same steroid for one week and referred to the Royal Surrey trust's emergency ear, nose and throat clinic – where his Bell's palsy diagnosis was confirmed.
A telephone follow-up two weeks later revealed "the symptoms had greatly improved and had almost returned to normal".
"The patient has been advised to discuss future mRNA vaccines [the technology used to develop the Pfizer-BioNTech and Moderna jabs] with the GP on a case-by-case basis, taking into account risk versus benefit of having each vaccine," wrote the medics.
Although it is unclear, the vaccine may "reactivate" a dormant virus lying within the central nervous system, "causing facial nerve inflammation or oedema [a build-up of fluid]".
The man had tested negative for coronavirus antibodies, a sign of a previous infection, on 16 June, 2020. It is unknown if he later caught the virus.
The vaccine may have also reactivated the herpes virus – which can lie dormant in the body for long periods – or the varicella zoster virus, which causes chickenpox.
The Royal Surrey medics have concluded: "The occurrence of the episodes immediately after each vaccine dose strongly suggests the Bell's palsy was attributed to the Pfizer-BioNTech vaccine, although a causal relationship cannot be established."
Speaking of the report, Professor Kevin McConway – from The Open University – said: "It's important to understand we can't even be certain from this case report that this patient's Bell's palsy episodes were caused by the vaccine.
"I think 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.
"Bell's palsy isn't common, but nor is it extremely uncommon.
"It's reported 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.
"My feeling is, 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 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 [the disease caused by the coronavirus]".
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