Every vaccine has its side effects, but most are mild and/or rare. If you’ve ever had a sore arm after a flu shot, or even a mild headache or fever, you’ve experienced these. The upcoming coronavirus vaccines will have side effects, too, and they might be a little more severe. That’s not necessarily a bad thing, though.
No COVID vaccine has yet been approved in the U.S., but we’re getting closer. One of the top candidates, the Pfizer/BioNTech vaccine, was just authorized for emergency use in the U.K. and could get a similar approval in the U.S. as early as next week. Another, from Moderna, is also under FDA consideration and could also be approved this month. (In both cases, the FDA will consider the safety and efficacy data and make a decision. There’s no guarantee a vaccine will be approved at all, but available information gives us reason to be hopeful.)
Fever and body aches may be common
Makers of both the top vaccine candidates have said that side effects from the vaccine are mild to moderate, which means (if that’s a complete and accurate statement) that they do not pose a serious safety risk. But mild and moderate side effects can still be uncomfortable.
According to the Pfizer vaccine’s UK label, the following side effects are very common, each affecting more than 10% of people who receive the vaccine: pain at the injection site, tiredness, headache, muscle pain, joint pain, chills, and fever. (Note that it’s not necessarily common to have all of these, just that each one is common individually.)
Up to 1 in 10 people may have redness and swelling at the injection site, or experience nausea. And more rarely, people have reported swollen lymph nodes and “feeling unwell,” whatever that means exactly.
For an example of what this looks like, we can look to a few accounts from volunteers in the trials. One person in a vaccine trial—who doesn’t know for sure if she got the real vaccine or a placebo—told MarketWatch that her arm hurt after she got her injection, making her think she probably got the real vaccine. “The day after I got injected, I felt sluggish and tired, with body aches,” she said. “About three weeks later, I received a second injection. Again, my arm felt sore, looked red at the injection site and I had body aches and fatigue.”
At a recent CDC advisory committee meeting, panelists discussed the importance of people understanding that these side effects can happen. You might end up taking a day off from work if you feel crappy, for example. Hospitals and essential businesses may need to account for this fact and, for example, probably shouldn’t vaccinate their entire ICU staff all at the same time.
Side effects mean it’s working
While it might be annoying to experience these symptoms, they’re not a sign of a problem. Vaccines work by spurring our immune systems to react to the faux invader. Fevers, tiredness, and muscle aches are part of our own bodies’ response to an infection, and a mini version of that response often accompanies a vaccine.
COVID is a severe enough disease that the annoyance of these symptoms is, for most of us, well worth the potential benefit of being protected from a severe infection. But if the vaccine is approved and you decide to get it, it’s important to be aware of the possible effects.
Public health experts are afraid that people who experience fevers or tiredness after their first dose might not want to come back for the second. That’s important because most of the vaccine candidates require two doses for full protection. The UK label for the Pfizer vaccine notes that you shouldn’t consider yourself protected until seven days after the second shot. Since the two doses are given at least three weeks apart, this means your protection won’t begin until a month after the first one.
We’ll probably find out more about the vaccines and their side effects around the time of their respective FDA meetings—Dec. 10 for Pfizer and Dec. 17 for Moderna. Stay tuned.