Moderna Caused This Reaction in 82 Percent of People, New Study Says

People who got the Moderna shot experienced this side effect more than those who got Pfizer.

When you sit down for your COVID shot, you know there's a pretty good chance you'll experience some side effects, but minor discomfort is a small price to pay to keep you and your loved ones safe. Still, it's important to know what you're getting yourself into so you can be fully prepared. A recent study found that there was one side effect that was extremely common for people who received the Moderna vaccine, with 82 percent of recipients reporting the reaction after the second dose. To see which side effect you should expect from Moderna, read on, and for more on this shot, This Is How Long the Moderna Vaccine Really Protects You, New Study Says.

After the second dose, 82 percent of Moderna recipients experienced a reaction at the injection site.

Woman with pain in upper arm

An April 5 study published in the Journal of the American Medical Association (JAMA) found that the overwhelming majority—82 percent—of Moderna recipients experienced a reaction to the vaccine at the site of injection after the second dose. After the first dose of the vaccine, 74 percent of Moderna recipients reported an injection site reaction. These reactions included pain, redness, swelling, and itching at the injection site. Pain was the most common site reaction, with 78 percent of Moderna recipients experiencing it after the second dose and 71 percent reporting it after the first.

Injection site reactions are to be expected with any of the vaccines, and experts say it's nothing to worry about. While this side effect is more common with Moderna, the study found that it still occurs in recipients of the Pfizer vaccine. The study found that 65 and 69 percent of Pfizer recipients reported injection site reactions after the first and second dose, respectively. The researchers noted that "injection site pain is common after both the first and second doses of either mRNA-based vaccine." And for more vaccine guidance, This Common Medication Can Make Your Vaccine Less Effective, Study Says.

The Moderna vaccine has a higher rate of reported side effects than the Pfizer vaccine.

Senior female recevies COVID-19 vaccination at the clinic

The study looked at reports from almost two million people who received both doses of either Pfizer or Moderna. According to the reports, which were collected through a Centers for Disease Control and Prevention (CDC) program called v-safe that tracks vaccine side effects, people who got the Moderna vaccine reported more side effects than those who got Pfizer.

"A greater percentage of participants who received the Moderna vaccine, compared with the Pfizer-BioNTech vaccine, reported reactogenicity [reactions that occur soon after vaccination]; this pattern was more pronounced after the second dose," the study reads. A higher percentage of Moderna recipients reported side effects in every single category. And to make sure you're ready after your shot, Be Prepared for This the Night You Get Your COVID Vaccine, Doctors Warn.

The biggest difference between the vaccine side effects was chills.

Woman home sick with fever covered in blanket
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The starkest difference in the percentage of recipients experiencing a side effect was in those who reported chills. Just 22 percent of Pfizer recipients reported having chills after their second dose, while almost double (40 percent) of Moderna recipients had chills after their second dose.

While 64 percent of people who got the second Pfizer jab reported systemic side effects—that is, not at the injection site—75 percent of Moderna recipients said they experienced these reactions. Fatigue, headache, muscle and joint pain, fever, nausea, vomiting, diarrhea, abdominal pain, and rashes were all more commonly experienced with the Moderna vaccine, according to the study. And for more COVID vaccine news delivered straight to your inbox, sign up for our daily newsletter.

Vaccine side effects are more common in younger people.

Young man suffering with fever and chills while sitting wrapped in a blanket on the sofa at home

The study found that people over the age of 65 were less likely to experience side effects than people under 65 with either vaccine. However, all age groups were more likely to experience side effects with the second dose of both vaccines.

According to Business Insider, this may be because immune systems tend to deteriorate over time, so older adults' bodies don't work as hard to protect them against foreign invaders, including the vaccine. And to avoid a more unpleasant reaction, Doing This After Your Vaccine Can Make Side Effects Worse, Doctors Say.

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