At the time of writing, there is no evidence to link the condition to the vaccine.
Bell's palsy is a condition that causes weakness or paralysis of the muscles in the face, which usually resolves itself in six months. Some social media posts have claimed that the Pfizer/BioNTech COVID-19 vaccine causes Bell’s palsy. However, a correlation between two events, phenomena, or variables does not imply causation.
On December 10, the U.S. Food and Drug Administration (FDA) held a committee meeting to discuss the emergency authorization of the Pfizer/BioNTech COVID-19 vaccine. Before this meeting, a 53-page briefing stated that there had been four cases of Bell's palsy among the group which received the vaccination and none among the placebo group. But, as USA Today reports, the annual incidence rate for Bell's palsy within the general population is around 23 cases per 100,000 people or 15-30 per 100,000 people. This means that the trial's four cases out of 38,000 trial participants come down to 11 cases per 100,000 people. Therefore, because the finding was "consistent with the expected background rate in the general population" the committee ruled there was "no clear basis upon which to conclude a causal relationship" between the vaccine and the occurrence of Bell's palsy.
The FDA recommends monitoring coronavirus vaccine recipients for Bell's palsy as the vaccines roll out, but the agency at this time does not have enough evidence to link the condition to the inoculations. Similar instances were noticed in the Moderna coronavirus vaccine trials, three in the vaccine group and one in the placebo group, but the FDA said that the rate it occurred in the trials is consistent with the background rate in the general population.
Moreover, a similar issue arose decades ago, when a few isolated cases of people developing Bell's palsy after getting a flu vaccine were reported. However, no study has ever established a link between the flu vaccine and Bell's palsy.
The exact cause of Bell's palsy is unknown, though it's thought to be caused by viral infections. Some 40,000 people in the U.S. experience the condition each year.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.