More people who received the Moderna COVID-19 vaccine reported side effects than recipients of the Pfizer shot, according to a recent study for the Centers for Disease Control and Prevention released in the online journal JAMA.
According to analysis of reports from over 3 million vaccine recipients by the CDC, almost 70% of those who received the Moderna vaccine said they experienced an adverse reaction at the injection site such as pain or swelling, while about half reported side effects like chills or fatigue.
“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 data taken from Dec. 14, 2020 to Feb. 28, 2021, about 74% of Moderna recipients reported an adverse reaction following a single dose, with 82% reporting side effects after the second dose, compared to 65% of Pfizer recipients after the first dose and 68% after the second.
Most of the side effects reported were minor, such as fatigue, headache, and pain at the injection site. More serious reactions such as abdominal pain and vomiting were relatively uncommon with the Moderna vaccine.
“The frequency of reported reactions was generally consistent with results observed in clinical trials. Data from millions of v-safe participants indicate that injection site pain is common after both the first and second doses of either mRNA-based vaccine. Systemic reactions, including fatigue, headache, myalgia, chills, fever, and joint pain, occurred in participants after the first dose, although they were more frequently reported after the second dose among both Pfizer-BioNTech and Moderna vaccine recipients,” the researchers noted.
The National Institutes of Health announced earlier this week that it will conduct a clinical trial of allergic reactions to the COVID-19 vaccines from Moderna and Pfizer, specifically “to determine whether people who are highly allergic or have a mast cell disorder are at increased risk for an immediate, systemic allergic reaction” after receiving either vaccine.
“The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech COVID-19 vaccines,” said Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, in a statement on Wednesday. “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. However, for most people, the benefits of COVID-19 vaccination far outweigh the risks.”