What We Know So Far About the New COVID-19 Booster Side Effects

Omicron-specific booster shots are here. And thankfully, more protection against COVID-19 doesn’t necessarily come with more intense side effects.

While scientists are still learning about the side effects of the new bivalent boosters, existing data appear promising. In earlier trials of similar bivalent vaccines, participants reported side effects that were on par with those experienced by people who got four doses of the original vaccine formulas.

For most people, the effects of the vaccine will be relatively mild and short-lived, said April Kapu, DNP, APRN, ACNP-BC, president of the American Association of Nurse Practitioners.

“In the clinic where I’ve been working, we have not seen any differences in side effects yet,” Kapu told Verywell. “But that’s still to come. We need to continue to follow the data over the next few months, as more and more people get the vaccination, but there’s no reason to believe that it would be any different.”

What Side Effects Should You Expect?

Neither Moderna nor Pfizer has reported human data on their BA.4/BA.5 bivalent boosters. Instead, federal regulators relied on animal studies and clinical trial data from an earlier bivalent booster shot for authorization.

The most common side effects for adults boosted with the BA.1 bivalent shot were arm pain at the injection site, fatigue, headache, muscle aches, and joint pain, according to trial data. More people reported having injection site pain after three doses of the Moderna vaccine than after three Pfizer doses.

Moderna said that compared to a second and third dose of its original formula, the BA.1 bivalent booster caused even fewer side effects.

Pfizer reported similar outcomes. Side effects were similar between patients ages 55 years and older who received a fourth dose of the original vaccine formula and those who got a BA.1 bivalent shot as their fourth dose.   

While the booster rollout is just starting, no one receiving the Omicron-specific vaccine has reported side effects not already seen after other COVID-19 vaccinations.

“There’s nothing different in terms of the side effects that are being reported—most often it’s redness at the site of the inoculation, some soreness, often feeling tired for a day or two afterward—all the same side effects we’ve seen at relatively the same rates with the bivalent booster,” Andrew Pekosz, PhD, a virologist at the Johns Hopkins Bloomberg School of Public Health, said in a press briefing.

According to the government’s vaccine safety tracker, called V-Safe, fewer people reported a change in their wellbeing after a shot of the original booster than after the primary series doses. And in people 50 years and older, the second booster shot seemed to cause even fewer reactions than the first.

The CDC recommends anyone 12 years and older get the updated booster shot at least two months after their last dose of vaccine or at least three months after recovering from a COVID-19 infection.

While it’s perfectly safe to get the bivalent booster two months after your last vaccination, waiting four to six months may help your body build a more durable immune response, Pekosz said.

What If You Get a Flu Shot at the Same Time?

The side effects of the flu shot and COVID-19 boosters are very similar. They both tend to cause soreness and redness at the injection site, headache, fever, and muscle aches.

When COVID-19 vaccines first became available, experts recommended getting that shot and the flu vaccine at different times, so that if there were complications, health providers could more easily pinpoint which vaccine had caused the problem.

Since then, Kapu said getting both shots at the same time has been shown to be safe, and doing so generally doesn’t worsen the side effects.

Federal health officials are encouraging people to get their updated COVID-19 booster and flu shot at the same time, in part to increase uptake of each. But, according to STAT writer Helen Branswell, it’s still early in the flu season, and getting your flu shot now may mean losing some immunity by the time flu season peaks around February or March next year.

What About Myocarditis and Pericarditis Risks?

With each vaccine authorization, regulators are mindful of the risk of myocarditis, a rare type of heart inflammation that has occurred in a few cases after vaccination.

Research indicates that extending the interval between mRNA vaccine primary series doses could reduce the risk of heart inflammation in this group.

Males ages 12 to 29 years are at the highest risk of developing heart inflammation in response to the vaccine. According to a government safety tracker, the risk of myocarditis in young males is lower after the first booster dose compared to after the second primary shot of either vaccine.

People in this age group should consult with a health provider about when is the best time to get the updated booster, said Kenneth Campbell, MPH, DBe, an assistant professor at Tulane University’s School of Public Health & Tropical Medicine.

“There still many unknowns for patients with potential risk in this population of young men, specifically with these new bivalent boosters,” Campbell said. “Based on what is known, most individuals with myocarditis have fully recovered at follow-up.”

How to Cope With Side Effects From the Booster Shot

As with the primary series and first booster shot, side effects typically emerge in the first 24 hours after the vaccination. Fever, chills, swollen lymph nodes, and muscle aches may pop up in the first 12 hours and should subside within 48 hours. It’s normal for a sore arm or fatigue to linger a bit longer.  

If you continue to experience flu-like symptoms or other vaccine side effects three days or more after getting the shot, Campbell recommends speaking with a health provider.

In reports from people who received their first booster, more than 89% of the side effects in people older than 12 years were non-serious.

“The side effects can vary from person to person. In many cases, there is some discomfort but you are able to continue your daily routines,” Campbell said.

The CDC said it can be useful to take over-the-counter pain medication, like ibuprofen or Tylenol, to help manage fever and pain after the shot. However, the agency said not to try and prevent side effects by taking one of these pain relievers before the vaccination, as scientists don’t know whether they change the effectiveness of the vaccine.

Cooling the injection site with a wet washcloth and exercising the arm can help ease swelling and tenderness.

“Allow your body to heal and build up its immunity,” Kapu said. “Take it easy for a couple of days. Rest and drink plenty of water.”

Symptoms should resolve within a day or two. If you’re still feeling the effects of the vaccination after that point, it may make sense to talk with a health provider. If you’re experiencing other common COVID-19 symptoms, consider taking a COVID-19 test to see if you’re infected.

“People have different concerns and it can be very individual,” Kapu said. “Don’t hesitate to reach out to your NP or nurse on call or your health care provider and ask those questions.”

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.