Both Pfizer and Moderna's vaccines have been vetted by the FDA, and so far they look very safe and effective at preventing COVID-19 infections, based on trials in tens of thousands of volunteers around the world.
Common side effects after vaccination have included arm pain, fatigue, and headaches, which last a few days, but no major safety concerns have been raised yet.
Still, some concern has been voiced about a potential connection between the vaccines and Bell's palsy, a temporary facial paralysis, after 7 cases of the condition were reported among vaccine recipients.
"At this point, there's no evidence to support that these vaccines trigger an increased risk of Bell's palsy, it's really important for the public to understand that," one otolaryngologist said.
Visit Business Insider's homepage for more stories.
By now, hundreds of thousands of people around the world have gotten injections of Pfizer's new COVID-19 vaccine, which was deemed both safe and effective enough for a Food and Drug Administration emergency use authorization during the pandemic.
Before the shot was released to the public, more than 20,000 volunteers around the world tried it out over a period of several months, with no major safety concerns reported among trial volunteers from the US to Argentina, South Africa, Germany, Brazil, and Turkey. Common — but temporary — side effects reported in the trials included pain at the injection site (in the arm), fatigue, and headaches, generally lasting about a day or two post-jab.
The same was generally true of Moderna's new coronavirus vaccine, which was also tested out in more than 15,000 volunteers across the US.
Both shots were deemed more than 94% effective at preventing symptomatic coronavirus infections, making them critical disease-fighting tools at this stage in the pandemic. The coronavirus is now among the leading causes of death in the US, killing more than 3,000 people across the country every day.
However, some concerns have been raised about seven people who received the vaccine in trials from Pfizer and Moderna, who developed a temporary form of facial paralysis called Bell's palsy.
What is Bell's palsy, and is it a concern?
The condition involves a sudden weakness of the face, usually on one side. Why this happens isn't well understood, although the paralysis is linked to inflammation of facial nerves.
People with Bell's palsy may have trouble closing one eye, wrinkling their forehead, or pulling up the corner of their mouth to swallow food. Most people make a full recovery in six months or less.
The FDA has said that it can't rule out with absolute certainty that Pfizer and Moderna's vaccine did not have an impact on these seven cases, and the agency will continue to investigate the issue. But based on the evidence we have, there's no reason to think the vaccine caused the facial paralysis, according to Dr. Nate Jowett, director of the surgical photonics & engineering laboratory at Mass Eye & Ear, and an associate professor of otolaryngology at Harvard Medical School.
"At this point, there's no evidence to support that these vaccines trigger an increased risk of Bell's palsy, it's really important for the public to understand that," Jowett told Insider.
The number of cases is small enough to be explained by coincidence