More side-effects were found in people taking the Moderna’s coronavirus vaccine than those who got the Pfizer shot, according to a recent study published on Monday, April 5, 2021, in the peer-reviewed medical journal JAMA.

Researchers analyzed information between December 14, 2020, and February 28, 2021, from more than 3 million vaccine recipients collected via v-safe, a Centers for Disease Control and Prevention program that tracks reactions to the immunizations. 

People who enrolled in v-safe are prompted to fill out a daily survey via a text message-based program about any symptoms, like fatigue or arm pain.

Overall nearly 70 percent said they had some injection site reaction, like pain or swelling, and 50% reported general side-effects like fatigue or chills, the study found.

“A greater percentage of participants who received the Moderna vaccine, compared with the Pfizer-BioNTech vaccine, reported reactogenicity, this pattern was more pronounced after the second dose,” the researchers noted.

In terms of the injection site reaction, 73 percent of those who received the first Moderna injection reacted, compared to 65 percent of those who received Pfizer’s vaccine. Nearly 82 percent of those who received their second Moderna shot reported the symptoms compared to under 69 percent of those who received their second Pfizer vaccine, which widens the gap.

Regarding full-body symptoms, nearly 51% of the first Moderna recipients said they reacted, compared to 48% of those who received the Pfizer injection. After the second injection, 74 percent of Moderna recipients showed symptoms, compared to 64 percent of the second Pfizer vaccine.

As to chills, 40 percent of second Moderna recipients reported it, compared to just 22 percent of second Pfizer recipients.

The above research was conducted with data collected from over 3.6 million individuals who received their first injection of the covid-19 vaccine before February 21, 2021, and completed at least one health survey on v-safe within seven days of receiving the shot. After the second dose, data collected from the reaction was from about 1.4 million people who completed those check-ins after receiving the second shot.

The study discovered that the response was most potent on the first day after injection with both vaccine doses and gradually decreased until day seven.

It also found that people under 65 showed more side effects to v-safe than those 65 and older, which is a typical finding for vaccinations.

Vaccine side effects are more common in women and younger people in general.

“That’s not to say they have more symptoms, however,” Stanford University infectious disease physician Anne Liu said, adding that it’s likely that younger people, especially women, report their symptoms with greater frequency.

It’s possible that younger individuals have more robust immune systems, suggesting why they have more symptoms.

“Older people’s immune systems tend to get weaker over time,” Liu explained, meaning their reaction to the vaccine will be less intense.

“If you have no side effects, you may have a weaker response,” Liu said.

Following the paper’s publishing, the National Institutes of Health (NIH) announced the start of a parallel study to look at the cases of allergic and anaphylactic reactions after receiving a dose of the Moderna or Pfizer vaccine.

“The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech COVID-19 vaccines,” said Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH. “The information gathered during this trial will help doctors advise people who are highly allergic or have a mast cell disorder about the risks and benefits of receiving these two vaccines.”

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