A video on Youtube and a post on Facebook have claimed that four volunteers taking part in the Pfizer-BioNTech Covid-19 vaccine trials were left with Bell’s palsy after participating.
Bell’s palsy is a weakness or paralysis of one side of the face which is usually temporary, and treated with steroids. The exact cause isn’t known but it’s thought to have something to do with the herpes virus.
It’s true that four people who received the vaccine during trials later got Bell’s palsy, but that doesn’t mean the vaccine caused it. The trials in which this occured included 38,000 participants. Although all four people who got Bell’s palsy were in the group who got the vaccine (rather than a placebo), this is not more than we would expect to develop Bell’s palsy in a group of this size by chance.
According to the US Federal Drug Administration (FDA), these cases occurred at 3, 9, 37, and 48 days after vaccination.
Because these trials were so large, a number of people would be expected to get ill over the period covered by the trial. These illnesses won’t necessarily have been caused by the vaccine, but these kinds of incidents are closely monitored in case they are linked to the vaccine.
But in this case, there is no evidence that the vaccine is in any way linked to Bell’s palsy, because if you monitored a group of people this size and they hadn’t had the vaccine, this is about how many people you might expect would develop Bell’s palsy.
The FDA’s document on the vaccine explained it this way: “The observed frequency of reported Bell’s palsy in the vaccine group is consistent with the expected background rate in the general population, and there is no clear basis upon which to conclude a causal relationship at this time, but FDA will recommend surveillance for cases of Bell’s palsy with deployment of the vaccine into larger populations.”
This doesn’t mean scientists monitoring trials won’t keep observing these sorts of things. And as with all vaccines in the UK, the vaccine’s safety will be continually monitored as it is rolled out to the public, via the yellow card scheme (where information about potential side effects and adverse reactions are monitored and evaluated).