A Timeline of COVID-19 Vaccine Side Effects

If you’re getting ready for the first, second, or booster dose of your COVID-19 vaccine, you may wonder about what side effects to expect and how to deal with them.

Some side effects happen right after your shot, like mild pain in your arm. Others may take hours to develop. Remember that with the two-dose vaccines like Pfizer-BioNTech and Moderna, you may notice more side effects after the second shot.

This article offers a step-by-step timeline of possible symptoms to help you understand what to expect after the jab.

Right After Vaccination

The COVID vaccines are intramuscular, or "IM" for short. That means the liquid in the syringe goes directly into a muscle when the needle goes in.

Your body's immune system sees this as a threat, and pain at the injection site is part of its response. That's why your arm may feel sore, turn red, or swell a bit. Some people who get the Moderna vaccine may experience "COVID arm," a delayed skin reaction with raised, red welts on the arm.

The mild pain that COVID-19 vaccines may cause is similar to what some people report after the tetanus vaccination, Michelle Barron, MD, senior medical director of infection prevention and control for the University of Colorado Health, tells Verywell.

The Centers for Disease Control and Prevention (CDC) recommends placing a cool, wet washcloth over the area to help ease any pain. Moving or exercising your arm also may help.

15 Minutes After Vaccination

The risk of anaphylaxis—a severe allergic reaction to the vaccine—is lower just 15 to 30 minutes after vaccination. This reaction is very rare, but the CDC requires everyone who gets the vaccine to wait in the clinic for 15 minutes after getting the shot, just in case it happens.

“If you've had allergic reactions in the past, we want people staying for 30 minutes,” Kate Mullane, DO, PharmD, professor of medicine and infectious disease specialist at the University of Chicago, tells Verywell.

12 Hours After Vaccination

Other side effects may start within a few hours, or up to 12 hours after the shot. People commonly report systemic side effects, like fever, headaches, muscle aches, joint pain, chills, and fatigue.

In the Pfizer-BioNTech vaccine trials, more than 77% of participants reported at least one systemic reaction. The most common were fatigue, headache, and new or worsened muscle pain.

Some less common side effects include nausea and swollen lymph nodes (especially in the armpit).

There's no need to worry about any of the flu-like symptoms. The side effects mean your body is working hard to build the antibodies and cells it will need to fight the virus, if or when you are exposed to it.

“Although you feel terrible, it's a good thing, because those systemic effects are telling you that your body is making an immune reaction,” Mullane says.

12 to 48 Hours After Vaccination

Once these body-wide side effects set in, they can last for 12 hours or more. Experts say these side effects should all stop within 24 to 48 hours after your shot, though you may still have some slight fatigue or arm soreness after that.

Mullane says it’s best to avoid important events or take on key tasks the day after your vaccination if you’re concerned about the side effects. That's because your vaccine appointment and the window for peak symptoms aren't likely to happen at the same time. Most side effects come later.

It’s OK to take an anti-inflammatory medication like Tylenol or ibuprofen to relieve any symptoms. But Mullane says not to take it before the shot, as it can interfere with your immune response. 

After 48 Hours

If you still have severe symptoms two full days after your vaccination, you may want to talk with your doctor to see what to do next. It’s possible that while you had vaccine side effects, you were also ill with COVID-19 or a different infection.

“If the symptoms persist beyond the 48 hours and aren't getting better, or if you develop any kind of respiratory symptoms, you should get evaluated,” Barron says.

It’s important to note that you cannot get COVID-19 from any of the approved vaccines. However, it can take up to two weeks after the second shot of the two-dose vaccines, or the single dose of the Johnson & Johnson, to mount a full immune response.

A COVID infection and its symptoms are still possible until the end of this two-week waiting period. It also is possible to have a breakthrough infection, which means you have COVID even though you got the vaccine.

Side Effects Vary

When you hear about other people's experiences, remember that the vaccine side effects can vary greatly. Barron says that, in general, the side effects reported in the clinical trial data are the same as what people say after getting their own vaccines. 

“In the clinical trials, younger people were more likely to have reactions than older people,” Barron says. “They tended to have more of the systemic symptoms like the fever and chills and older people just reported a little bit of fatigue and arm soreness.”

“The healthier you are, the more in tune your immune system is, the higher the likelihood that you're going to have side effects because your immune system gets turned on,” Mullane adds.

If you don’t have intense side effects, like a high fever or body aches, it doesn’t necessarily mean your body won’t be protected against the virus. The time or intensity with which people’s immune systems respond to vaccines can differ based on many factors.

While the side effects can cause some pain and discomfort, Barron says that these effects are far better than the risks of getting sick with COVID-19.

“Forty-eight hours of side effects versus potentially the risk for hospitalization and death—I sort of think that favors the vaccine,” Barron says. “If there's any hesitation because of side effects, I’ll say the disease is far worse…or has the potential to be far worse.”

Summary

The best way to prepare yourself for a COVID vaccine is to learn about the possible side effects to expect. For most people, this means some mild symptoms like a sore arm, or flu-like symptoms that last up to two days before going away.

In rare cases, a serious reaction or complication may follow COVID vaccination. That's not a reason to avoid a vaccine because the benefits still outweigh the risks, but it is a good idea to keep a close eye on how you feel after getting your shot.

Call your doctor if you think your symptoms are serious.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.