A: While we don’t yet know for sure, it does not look like the Pfizer-BioNTech or Moderna COVID19 vaccines cause Bell’s palsy.
Bell’s palsy is a condition that causes weakness on one side of the face. The facial nerve (the seventh cranial nerve for all of you keeping track out there) is responsible for movement of the forehead, eyelid, cheek and mouth as well as taste for the front 2/3rds of your tongue. When that nerve becomes damaged or swollen, an individual can develop Bell’s palsy. That person might have reduced or absent movement of one side of the face with difficulty closing the eye and decrease in taste.
Bell’s palsy is a pretty common condition and occurs in about 15-30 out of every 100,000 people. In the COVID19 vaccine trials, the rates of developing Bell’s palsy were the same as what we call the “background rate” (or the rate that would happen in the absence of any inciting event). There were 4 cases of Bell’s Palsy in the Pfizer-BioNTech trial out of 18,801 people who got the vaccine and 0 cases out of the 18,785 people who received the placebo. In the Moderna trial, there were 2 cases out of 15,185 people in the group that got the vaccine and 1 case out of 15,166 people in the group that received the placebo. Combined, this means that 17.7 out of every 100,000 people who received the vaccine develop Bell’s Palsy (just like the “background rate” above!). This led the FDA and medical professionals to say that there is no current evidence of any causal link between the vaccine and Bell’s palsy, and those folks most likely just happened to get Bell’s palsy coincidentally around the time of vaccination.
So, if it isn’t the vaccine that causes it, what does? Most often, clinicians don’t find a clear cause of Bell’s palsy. There are lots of potential causes, like the herpes simplex virus (herpes), diabetes, other viruses (like cold and flu viruses), and injury to the nerve itself.
Even though a specific cause isn’t always found, Bell’s palsy usually gets better in 1-2 months. It is typically treated with steroids and sometimes an antiviral medication. And, importantly, if someone had Bell’s palsy in the past, they can still get the COVID19 vaccine.
Of course, vaccine safety monitoring is ongoing, and we will get more and more info over time. Check our earlier post on vaccine safety monitoring.
American Academy of Otolaryngology – Head and Neck Surgery statement on Bell’s Palsy and Covid19 vaccines