En español | The news about the coronavirus vaccine has been positive lately. Many health care workers around the country received their first dose of the Pfizer-BioNTech vaccine after it acquired emergency use authorization (EUA) from the U.S. Food and Drug Administration (FDA) on Dec. 11. And the distribution of a second vaccine, from biotech firm Moderna, is underway now that it has cleared the same regulatory hurdle. If all goes as expected, as many as 20 million Americans could be vaccinated against COVID-19 before the end of the year.
While it may take a while for production to ramp up to the point where a vaccine is readily available to the general public, health experts say there is one thing that’s critical for people to understand before they roll up their sleeves for the shots: The vaccines may cause side effects. According to the FDA, the most common side effects among participants in both the Pfizer-BioNTech and Moderna phase 3 clinical trials were:
- Injection site pain
- Muscle pain
- Joint pain
However, these reactions are “temporary,” and they “self-resolve” within a few days, says Wilbur Chen, M.D., a professor of medicine and chief of adult clinical studies at the Center for Vaccine Development and Global Health at the University of Maryland. Even so, it’s “ultracritical” that health experts are transparent with the public about what to expect.
“Where a mistake could be made is in people being surprised or not being prepared for side effects,” adds William Moss, M.D., executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health.
Transparency builds trust
One reason: public trust. Polls show that as many as 42 percent of Americans say they are unwilling to get a coronavirus vaccine when one becomes available, for reasons spanning the unprecedented speed of the vaccines’ development to a general mistrust of vaccines. People are also concerned about potential side effects from the shots, according to a recent Pew Research Center survey, making it “critically important” for health experts to be upfront about all the possibilities, Moss argues.
Another reason people need to know about any potential side effects: Both the Pfizer-BioNTech and Moderna vaccines require two doses, given a few weeks apart. And unanticipated side effects from the first shot could deter people from going back for the second, which is needed to “get the most protection the vaccine has to offer,” the Centers for Disease Control and Prevention (CDC) points out.
“We don’t know what happens after a single dose,” Moss says. “Certainly we can’t expect [that one dose will confer] the high degree of protection” that both doses demonstrated in phase 3 clinical trials. (Pfizer’s vaccine, for example, was found to be about 52 percent effective after the first dose; effectiveness jumped to 95 percent after the second.)
“So it’s really important that people get two doses and not be thrown off or discouraged,” Moss adds.
Finally, knowing that a sore arm or a fever is a possible side effect helps ease public alarm, says Hana El Sahly, M.D., associate professor of molecular virology and microbiology at Baylor College of Medicine. If someone experiences an unpleasant, but expected, response, “they can take some symptomatic treatment and have reassurance and minimize their anxiety around the vaccine,” she explains.
Side effects are not unique to COVID-19 vaccine
Side effects from vaccines are not uncommon. The seasonal flu shot, for example, can cause fever and fatigue, among other reactions. And the vaccine to prevent shingles can induce shivering, muscle pain and an upset stomach, to name a few.
In some ways, these mild to moderate reactions are “a good thing,” Moss says, because “it’s a sign that the immune system is responding to the vaccine.” Nevertheless, they shouldn’t be downplayed. For some people, a sore arm “is a big deal,” Chen points out. Reactions from the coronavirus vaccine may even cause recipients to miss a day or two of work.
The key, experts say, is to weigh the temporary discomfort against the long-term benefits: a potentially high level of protection from a disease that has uprooted everyday life for many of us and has killed more than 1.6 million people globally.
“We are willing to tolerate discomfort in other aspects of our life — many people exercise and have muscle aches afterward, and don’t say, ‘I’m never going to exercise again,’” Moss points out. “There are just many aspects of our lives where we need to be willing to make the trade-off for some degree of discomfort for a longer-term gain.”
It’s also important to keep in mind that the majority of reactions occur shortly after vaccination, so “there is a degree of reassurance” that the side effects reported in the clinical trials are likely the extent of any unpleasant short-term reactions, El Sahly says.
Older adults could experience fewer side effects
An interesting finding from the Pfizer-BioNTech and Moderna clinical trials is that while the vaccines seem to be just as effective in older adult participants, people 65 and older experienced fewer side effects than younger volunteers.
Researchers are still studying why this is the case, but it could have something to do with the declining immune response that comes with age. Because the coronavirus vaccine can provoke “a little bit of an inflammatory response,” Chen says, it may be that older adults react less to the medicine if they have “a blunted immune response already.”
Reports of a few adverse events
Federal analyses of both vaccine trials show that few adverse events — which the CDC defines as any health problem that happens after a shot — separate from the less serious side effects were reported. Swollen lymph nodes (lymphadenopathy) occurred in a small portion of the participant population. And four people who received Pfizer’s vaccine and three who received Moderna’s developed Bell’s palsy, which, in most cases, causes temporary weakness or paralysis in the face.
FDA scientists have said that the documented cases of Bell’s palsy are “consistent with the expected background rate in the general population” and that “currently available information is insufficient to determine a causal relationship [between Bell’s palsy and] the vaccine.” However, the situation is worth monitoring, health experts say.
Some people have also reported severe allergic reactions — known as anaphylaxis —after receiving the Pfizer-BioNTech vaccine. (Large-scale vaccination efforts haven’t started yet with Moderna’s product.) Because of this, the CDC is recommending that anyone who has ever had a severe allergic reaction to any ingredient in a COVID-19 vaccine abstain from receiving it. (You can find the ingredients of authorized vaccines on the FDA's website) If you have a history of severe allergic reactions to other vaccines, ask your doctor if you should get a COVID-19 vaccine, the agency advises.
People with a history of severe allergic reactions not related to vaccines (allergies to food, pets, latex, etc.) may still get vaccinated. The same goes for people with a history of allergies to oral medications and those who might have a milder allergy to vaccines (no anaphylaxis), the CDC says. Just be prepared to be monitored on site for about 30 minutes after the shot.
If you get a COVID-19 vaccine and experience an allergic reaction, seek immediate medical attention. And if you have a severe allergic reaction after getting the first shot, you should not get the second shot, health officials advise.
Finally: It’s important to keep in mind that these reactions, though serious, are relatively rare, seeing how tens of thousands of people have been inoculated with one of the two vaccines. “It’s a warning for a very small number of people,” says Barry Bloom, professor of public health in the department of immunology and infectious diseases at Harvard’s T.H. Chan School of Public Health.
If you’re concerned that your allergies could trigger a severe reaction to a coronavirus vaccine, talk to your doctor. And consider getting your vaccine in a medical setting, in case you do react and need immediate care.
“Most people can get the vaccine at pharmacies or a variety of different places. For people who’ve had allergic reactions, it’s a reason why they should talk to their doctor first — they [may] want to go to a place that’s more equipped for serious allergic reaction,” Karyl Rattay, director of the Delaware Division of Public Health, said in a recent news conference.
Safety monitoring doesn't stop when vaccines become available
Just because the vaccines have expanded from trial participants to the public doesn’t mean monitoring for them will stop. Individuals who receive the vaccines will continue to be watched for long-term side effects and adverse events or disease. This follow-up will also give researchers more information on how long immunity to COVID-19 lasts after vaccination.
Something else that won’t stop when the vaccines are rolled out: the recommendation that people continue the prevention efforts that can help slow the spread of the disease, including mask wearing, social distancing and frequent handwashing. That’s because it typically takes a few weeks for the body to build immunity to a disease after vaccination, according to the CDC, meaning it’s possible you can get sick with COVID-19 even after you’ve been vaccinated. Plus, experts still aren’t sure whether the vaccines, which are highly effective at preventing COVID-19, block transmission of the virus.
Finally, it takes time to build up what Chen calls “community immunity,” or herd immunity, where enough of the population is protected from the virus that transmission slows significantly. Experts are not sure what the magic number is to obtain herd immunity for COVID-19, but they estimate it’s somewhere around 70 percent of the population, which could take months to achieve through vaccination.
“And before that, I don’t think anyone can let their guard down,” El Sahly says.
Editor's note: This story, originally published Dec. 2, has been updated to reflect new information.