Moderna Says These Are the Side Effects to Expect From Its Booster Shot

A new trial found that these are the most common reactions to the booster shot.

While people across the country get their first round of shots, the pharmaceutical companies responsible for the approved COVID vaccines in the U.S. are already looking ahead to boosters. These future shots will help bolster your immunity and protect you from emerging COVID variants. Moderna just shared findings from clinical trials that show promising results for its booster shot, along with the most common reactions among participants. Read on to see what side effects you should expect from a Moderna booster shot, and for more on the future of vaccination, This Is When You'll Need a Third COVID Shot, BioNTech CEO Says.

Side effects of the Moderna booster shot are similar to second dose side effects.

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On May 5, Moderna shared a statement that highlighted the findings of clinical trial data on its booster shot. Researchers found that the Moderna booster helps protect against new variants and provides continued immunity from COVID. If you thought you were done dealing with vaccine side effects after your second shot, however, this research says otherwise.

According to the statement, the side effects of the booster shot are similar to those experienced after the second dose of the vaccine. The most common side effects included pain at the injection site, fatigue, headache, muscle pain, and joint pain. Moderna did note that, in general, people reacted less to the booster shot than to the original vaccine. And for more on the vaccine timeline, Pfizer's CEO Just Said How Often You'll Need a COVID Vaccine.

The most common side effect of any Moderna vaccine is pain at the injection site.

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According to the booster shot trials, the most frequently reported adverse reaction was pain at the injection site. And that makes sense, given that the most common reaction to the existing Moderna vaccine is also pain at the injection site, with 78 percent of people reporting it after the second dose, according to an April 5 study published in the Journal of the American Medical Association (JAMA). The second most common side effect was fatigue, with 60 percent of Moderna recipients reporting the reaction after the second shot.

Other common side effects to the current Moderna vaccine include redness, swelling, and itching at the injection site, headache, chills, fever, nausea, joint pain, and muscle pain. Less common but notable side effects include vomiting, diarrhea, abdominal pain, and a rash. And for more on how vaccination could change, Moderna CEO Says There Could Be a Big Difference in Your Next Vaccine.

The booster shot will help protect against two key variants.

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The clinical trials indicated that the booster shot provides promising protection against the Brazil and South Africa variants of COVID, along with additional protection from the original virus. "As we seek to defeat the ongoing pandemic, we remain committed to being proactive as the virus evolves," Moderna CEO Stéphane Bancel said in the statement.

"We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants," Bancel added. "The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of [the booster] to induce immune memory." And for more COVID vaccine news delivered straight to your inbox, sign up for our daily newsletter.

The shot should be ready by the fall.

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Experts say that it's inevitable that vaccinated people will need a booster shot of the COVID vaccine to maintain immunity and add a layer of protection from variants. During an International Federation of Pharmaceutical Manufacturers and Associations briefing on April 23, Bancel said he predicts the booster will be ready by fall.

"We're working very hard to potentially have late summer, early fall, that boost for the variants authorized to be able to be used in the marketplace for boosting people," the Moderna CEO said. During the briefing, Bancel referenced the promising clinical data that was just released. And for more vaccine news, This One Vaccine May Protect You Against All Variants, New Study Says.

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