Vaccine Side Effects: 4 Things to Know

With millions of people across the United States vaccinated against the coronavirus disease 2019 (COVID-19) and many more to follow, questions about side effects are becoming part of daily conversations among families, friends and co-workers. Some people have reported no side effects, while others have reported temporary side effects such as headaches and fevers.

Here are four things you need to know about the side effects of the currently available COVID-19 vaccines.

1. Side effects are normal—but not everyone will have them.

Experiencing mild side effects after receiving a vaccine isn’t unusual, whether the vaccine is for COVID-19, the flu or something else, says UNC Health infectious disease expert Cynthia Gay, MD, MPH, who leads the Moderna clinical trial at UNC.

The most common side effects of the COVID-19 vaccines are mild tenderness, swelling and/or soreness at the injection site. Other symptoms include feeling tired and achy, a low-grade fever or a mild headache.

“Those are not worrisome. These mild symptoms are really your immune system telling you that the vaccine is doing exactly what we want it to do,” Dr. Gay says. “We want your immune system to respond to the vaccine and produce antibodies.”

Then, if you’re exposed to COVID-19, those antibodies are ready to recognize and bind to the coronavirus, resulting in either no infection or a less serious infection.

Side effects almost always last just one to two days, and not everyone has them. But don’t worry—even if you do not have any side effects from the vaccine, it’s still doing its job.

2. Side effects are more common after the second dose.

If you feel worse after your second shot than your first, that’s normal—and expected. The first vaccine teaches your body how to react to the virus.

“It’s tricking your immune system into thinking it’s seen the virus,” Dr. Gay says. “The second dose improves on that immune response. It mounts more of a response with the second dose, so it would make sense that you might have more symptoms after the second dose.”

3. Take headache medicine if you don’t feel well after your vaccine.

Simple self-care measures—and giving it a little time—should resolve any side effects. You’ll likely feel back to normal in less than 24 hours. Rest if you can. If you have a sore or tender arm, it can help to move it often. For headaches and body aches, you can take an over-the-counter pain reliever.

In this specific case, Dr. Gay recommends acetaminophen (Tylenol) instead of ibuprofen (Advil, Motrin) because ibuprofen is an anti-inflammatory and it’s actually a good thing for your immune system to mount an inflammatory response to the vaccine.

Talk to your doctor if you are concerned about any symptoms.

4. Mild side effects outweigh the risk of COVID-19.

While nobody likes to feel sick even for a brief amount of time, feeling achy or feverish for a day or so is better than severe symptoms from COVID-19.

“It’s all about weighing risk versus benefit,” Dr. Gay says. “The vaccines prevent you from getting really sick and having to go to the hospital. So it’s 24 hours of a mild symptom versus the risk of something much worse.”

Vaccination is also a key step to ending the pandemic for everyone; the more people who get vaccinated, the harder it will be for the virus to spread.

For more facts about the COVID-19 vaccines, visit