En español | As the coronavirus vaccine rollout continues across the country, health experts say one thing is critical for people to understand before they roll up their sleeves: The vaccines may cause side effects.
Three vaccines – developed by Moderna, Pfizer-BioNTech and Johnson & Johnson – have been authorized by the U.S. Food and Drug Administration (FDA) to combat the coronavirus. The Johnson & Johnson vaccine requires only one shot, while the others require two doses.
The side effects are similar for the three vaccines and are an indication that the vaccines are helping to build protection against disease. These are the most commonly reported side effects:
- Injection site pain and swelling
- Muscle and joint pain
- Delayed swelling, redness or a rash at the injection site
- Swollen lymph nodes (typically manifests as a lump in your armpit or above your collarbone)
Most of the reactions are temporary and resolve within a few days, according to the U.S. Centers for Disease Control and Prevention (CDC). Since you may feel under the weather, experts recommend not making any big plans for a few days after you get a dose of the vaccine.
“Where a mistake could be made is in people being surprised or not being prepared for side effects,” says William Moss, M.D., executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health.
CDC data released Feb. 19 indicated that the side effects from the Moderna and Pfizer-BioNTech vaccines were as expected and not serious among the vast majority of the first 22 million people who received them.
The Johnson & Johnson vaccine appears to be somewhat less likely to cause side effects than the other vaccines, Moss said. In its clinical trial data submitted to the FDA, the most common side effects were headache (39 percent), fatigue (38 percent), muscle pain (33 percent), nausea (14 percent) and fever (10 percent).
Side effects are a sign the vaccine is working
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.
In some ways, these mild to moderate reactions are “a good thing,” Moss says, because they are “a sign that the immune system is responding to the vaccine.”
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 2.5 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 of some degree of discomfort for a longer-term gain.”
Older adults could experience fewer side effects
While the coronavirus vaccines have been shown to be effective in older adults, people age 50 and older experience fewer side effects than younger recipients.
Only about 25 percent of people ages 50 to 64 and 4 percent of those ages 65 to 74 who received the Moderna or Pfizer-BioNTech vaccine between Dec. 14 and Jan. 13 experienced side effects, according to CDC data. Meanwhile, 65 percent of those under 50 reported a reaction.
The clinical trial data from the Johnson & Johnson vaccine showed a similar effect.
Researchers are still studying why this is the case, but they say it’s likely related to the declining immune response that comes with age.
Studies also show that most people experience more severe side effects after the second dose of the Moderna or Pfizer-BioNTech vaccine.
How to treat side effects
Although side effects may affect your ability to do daily activities, most should go away on their own after a few days, the CDC says. Plan for plenty of time to rest in the days immediately after you get a dose of the vaccine.
If you have pain or discomfort, an over-the-counter pain reliever such as a nonsteroidal anti-inflammatory drug (Advil, Motrin) or acetaminophen (Tylenol) can help you feel better, doctors say.
“If your fever is making you uncomfortable, taking acetaminophen or a nonsteroidal anti-inflammatory should bring it right down,” says Dean Blumberg, M.D., an infectious disease specialist at UC Davis Health in Sacramento, California.
The CDC advises against the use of pain relievers before vaccination “for the purpose of preventing post-vaccination symptoms.” So wait until after you are experiencing side effects to take any medication.
If you have a delayed reaction at the injection site – typically described as a rash, itchiness or redness that appears five to 10 days after vaccination – it’s likely a mild allergic reaction, Blumberg says. He recommends treating it with an over-the-counter antihistamine like Benadryl or a topical steroid like hydrocortisone.
Another side effect that may last more than a few days is a swollen lymph node, which may feel like a lump under your armpit or over your collarbone. The swelling is not harmful, but it can last a few weeks, Blumberg says. Eventually, it should go away on its own.
Few reports of adverse events
Federal analyses of first month of vaccine rollout showed that few adverse events — which the CDC defines as any serious health problem that happens after a shot — were reported.
In the first month of the vaccine rollout, there were about 4.5 severe allergic reactions (called anaphylaxis) per million doses administered, CDC data show.
Severe allergic reactions are “exceedingly rare,” the CDC said, and should not discourage people from getting vaccinated.
Because of this, the CDC recommends 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.)
The CDC recommends people with a history of anaphylaxis be observed for 30 minutes after getting the shot; other recipients should be observed for 15 minutes.
Safety monitoring doesn't stop
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.
One way health officials are tracking side effects is with an app called V-safe that you download to your smartphone. When you get your first dose of the vaccine, your health care provider will give you information about how to get started.
Infectious disease experts urge vaccine recipients to participate because it gives them important safety information about the vaccine. The daily survey takes only about 30 seconds, and the app protects your privacy by erasing your phone number after you take the survey.
Editor's note: This story, originally published Dec. 2, has been updated to reflect new information.