According to a CNBC report, after a handful of people who received either the Pfizer or Moderna COVID-19 vaccine developed Bell’s palsy, the US Food and Drug Administration (FDA) recommends that people self-monitor for the condition that causes drooping in one side of the face. The FDA, however, does not list the condition as a side effect. 

Out of 30,000 Moderna vaccine trial participants, four people developed Bell’s palsy. According to the FDA, it’s not clear whether the condition developed as a direct result of the vaccine; one of the four people received the placebo. But placebo doesn’t necessarily imply an inert saline injection. In fact, for the Oxford-Zeneca Covid vaccine, the control group received a meningitis and septicemia vaccine as a placebo, reports The Conversation. 

The University of Oxford’s Jeremy Howick writes on TheConversation.com “The problem is that [scientists] rarely know how to interpret side-effect information in trials because researchers rarely report what’s in [a] placebo.” 

Furthermore, Howick says that reporting placebo ingredients, specifically in vaccine trials, is not common. “This makes it difficult to tell what the true harms of the vaccine are. The same applies to most treatments tested in trials with unknown placebos,” adds Howick.  

An FDA statement regarding the Covid vaccine reads, “Currently available information is insufficient to determine a causal relationship with the vaccine.” 

In the Pfizer trial, which included 43,000 participants, there were also four people who developed Bell’s palsy—all four received the vaccine. 

While FDA staff said there wasn’t enough data to tie the cases directly to the shots, it warranted close scrutiny.

A major reason it’s not clear whether the vaccine is directly responsible for Bell’s Palsy is the fact that the condition did not develop immediately after the participants received the injection. FDA staff reported that the vaccinated participants experienced the paralysis between 22 days and 32 days following the shot. 

Bell’s palsy is most often temporary. While the exact cause is unknown, one possible explanation is swelling or inflammation of the nerves. Or, the condition may be caused by a virus. 

In other news, Al Jazeera reports that Moderna’s two-dose Covid vaccine appears set for emergency use authorization by the FDA, after the organization did not issue any concerns over the vaccine (Bell’s Palsy notwithstanding).