If You Get a Moderna Booster, Expect These Side Effects, New CDC Report Says

The latest data highlights what you might experience after a third COVID shot.

Health experts have been debating the need for booster shots over the past few months, with the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) recently authorizing a Pfizer booster for certain groups of people at high risk for severe COVID. This additional shot is only available to those who received the Pfizer vaccine for their first two doses. Moderna recipients are advised to wait until a booster dose is approved for their specific vaccine, which White House COVID adviser Anthony Fauci, MD, has said will likely come "relatively soon." But if you got Moderna and are waiting your turn, you can still prepare yourself for what the next shot will be like, thanks to new CDC research documenting the potential side effects of a Moderna booster.

RELATED: Moderna Now Says Vaccine Protection Goes Down After This Long.

On Sept. 28, the CDC published a report highlighting the experience of more than 22,000 voluntary v-safe registrants who filled out a health survey after receiving a third vaccine dose between Aug. 12 and Sept. 19. The agency's v-safe program allows people to report their vaccine reactions through their smartphone, and a little more than 10,400 people chronicled their experience after receiving three doses of the Moderna vaccine.

According to the report, local reactions to the Moderna booster were most common. More than 80 percent of those who received a third dose of this vaccine reported at least one local, injection site reaction. The most frequently reported local reaction was pain at the injection site, which 75.9 percent experienced. Other local reactions included swelling for 33.6 percent, redness for 25.2 percent, and itching for 20 percent.

A little more than 75 percent of those who got a third Moderna dose reported at least one systemic reaction. In terms of systemic side effects, the most frequently experienced was fatigue, which 61.8 percent reported. The other reactions included muscle pain for 49.8 percent, headache for 49 percent, fever for 36.4 percent, joint pain for 33 percent, chills for 31.3 percent, nausea for 18.8 percent, diarrhea for 9.9 percent, abdominal pain for 8.4 percent, rash for 2.3 percent, and vomiting for 2.2 percent.

In terms of the health impact, 35.2 percent of those who received this additional Moderna shot said they were unable to perform normal daily activities after it, and 13.7 said they were not able to go to work or attend school following the dose. But the researchers say this is expected and consistent with the reactions following Moderna's first two doses. Local reactions after the third dose were reported a little more frequently than after the second, while systemic reactions were actually reported less frequently following this additional shot.

"The patterns of adverse reactions observed after dose three of Moderna vaccine were consistent with previously described reactions after receipt of dose two," the CDC stated.

RELATED: For more up-to-date information, sign up for our daily newsletter.

More people appeared to experience reactions following a third dose of Moderna's vaccine than an additional dose of Pfizer, according to the report. Only around 70 percent of Pfizer recipients experienced at least one injection site reaction after the third dose, and only 65 percent reported at least one systemic reaction. This isn't any different from what occurred after the first two doses. An April study published in JAMA Insights found that those who got the Moderna vaccine experienced more side effects with both the first and second shot compared to those who got Pfizer.

The likely difference comes from how much mRNA is included in each of the vaccines. Moderna's vaccine has 100 micrograms, while Pfizer's only has 30 micrograms. This means the likelihood of side effects might change depending on what the FDA approves for Moderna's booster. According to reports, the agency is considering authorizing a smaller, half-dose shot of 50 micrograms for this booster instead of a full 100-microgram dose, which may result in fewer people experiencing reactions.

RELATED: The CDC Director Says If You Want a Booster, Don't Do This Right Now.

Filed Under