Side Effects From the COVID-19 Booster Shot

When the COVID-19 vaccines became available in early 2021, many experienced side effects—especially after people had their second dose. The Centers for Disease Control and Prevention (CDC) even addressed this, noting at the time that side effects from the second dose can be more intense than ones people experienced after their first shot. Those side effects, the CDC said, are normal signs that your body is building protection. And after two doses, the booster shot became available in October 2021.

The CDC also recommended additional doses for immunocompromised individuals, based on their age group and the type of vaccine they received. But additional doses and booster shots can come with side effects and many wonder—are they worse or better than the first or second vaccine dose?

Here's what you need to know about any symptoms you might feel after a booster or additional shot of a COVID-19 vaccine, according to experts.

What Do We Need To Know About COVID-19 Booster Shots?

The CDC started recommending booster shots as early as September 2021, since protection against the virus and the ability to prevent infection from different variants can decrease over time.

As of February 2022, everyone ages 18 and older is able to get a COVID-19 booster, and either the Pfizer or Moderna booster is fine, but the CDC recommends that youth ages 12-17 only get the Pfizer booster. You should wait 5 months after being fully vaccinated to get the booster (2 months if you received the Johnson & Johnson Janssen vaccine).

Additional doses of the Moderna mRNA COVID-19 vaccine for individuals who are moderately to severely immunocompromised are different from booster doses, per the CDC: "Sometimes people who are moderately to severely immunocompromised do not build enough (or any) protection when they first get a vaccination," the agency said. That additional dose can then help immunocompromised people have a better chance of mounting some sort of immune response to the virus. A "booster dose," on the other hand, is a dose given to someone who was able to build protection after their initial vaccination, but then that protection decreased over time (aka, "waning immunity").

The CDC reiterates additional doses, as well as booster shots, for immunocompromised individuals should be administered based on your age group and the type of vaccine you received.

What Side Effects Can You Expect After an Additional or Booster Dose of the COVID-19 Vaccine?

"Whether you're getting an additional dose of a COVID-19 vaccine due to your immunocompromised status, or if you're receiving a booster shot, you can probably expect to have a similar (or possibly better) response to how you reacted after having the two-dose series of the vaccine," William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, told Health. "There is no tendency to have more side effects with a third dose than either the first or the second," said Dr. Schaffner. "What's clear is that it should not be worse."

Infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, agreed: "The side effects are probably going to be very similar to the second dose for most people," Dr. Adalja told Health. And, if you didn't feel so hot after your second dose, keep this in mind: Your third dose likely won't be as bad. "You may have less of a reaction because there is a lot of space between the second and third doses [versus] first and second doses," Dr. Adalja said. "Your immune system may be dampened somewhat."

In study findings released on September 28, 2021, the CDC reports that reactions reported after a third dose of the mRNA vaccine were "similar" to those of the two-dose series. The most common side effects have been pain at the injection site, fatigue, and headache. Most of these side effects were "mild to moderate" and happened a day after the booster.

Pfizer offered some detail in its application for an emergency use authorization (EUA) for a third dose, too. That application said that side effects after the third dose were similar to those after a second dose of the vaccine, including:

• Redness and swelling around the injection site
• Tiredness
• Headache
• Muscle and joint pain
• Chills

Pfizer also said in a 2021 press release about its EUA application for a booster dose that side effects were "similar to or better than" people had after their second dose of the vaccine.

What Can You Expect After an Additional or Booster Dose?

There's been a lot of expert advice about planning to take it easy after your second dose of the COVID-19 vaccine, and doctors say it's probably not a terrible idea for your third dose, just to be safe.

"It's sensible to take it easy afterward," Dr. Schaffner said. "Don't plan to do anything strenuous the day after your shot."

Dr. Adalja said you can expect to have a similar reaction to your second dose of the mRNA vaccine. "However rough it was, use it as your baseline to see if you need to take any special precautions," said Dr. Adalja.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.