The anecdotal reports are true: people who get the Moderna COVID-19 vaccine say they have more side effects than people who get the Pfizer / BioNTech shots, according to new data published this week in JAMA.
The study analyzed reports collected through a Centers for Disease Control and Prevention program called v-safe. It’s a text message-based program designed to track side effects in vaccine recipients. For the first week after each vaccine dose, people who enroll are prompted to fill out a daily survey about any symptoms, like fatigue or arm pain.
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Over 3,600,000 people who got their first dose of a COVID-19 vaccine before February 21st enrolled in v-safe and checked in at least once. Around 70 percent of those people said they had some kind of injection site reaction, like pain or swelling, and half had a more generalized reaction like fatigue or chills. For both, people who got a Moderna shot were more likely to have a side effect — 73 percent had an injection site reaction, compared with 65 percent of people who had a Pfizer / BioNTech dose. Around 51 percent of Moderna recipients had full-body symptoms, compared with 48 percent of people who got Pfizer / BioNTech.
The gap widened after the second dose. About 1.4 million people completed those check-ins. Almost 82 percent of people getting their second Moderna shot had injection site pain versus just under 69 percent of people with Pfizer / BioNTech. Overall, 74 percent of people said they had general reactions after their Moderna shot, compared with 64 percent of people getting Pfizer / BioNTech. The biggest difference was for chills, which were experienced by 40 percent of people taking Moderna and only only 22 percent of people taking the Pfizer / BioNTech shot.
People over 65 were also less likely to have side effects than people under 65, regardless of which vaccine they received.
The study didn’t include information on how severe participate said side effects were, so it’s not clear if one vaccine triggers more disruptive effects than the other. In addition, the people using v-safe may not be a representative sample of people getting shots. Only around 10 percent of people signed up for the program after they were vaccinated.
Overall, the side effects and frequency of side effects were similar to the ones seen in clinical trials testing these vaccines. The clinical trials gave researchers and doctors an accurate look at the types of side effects people can expect after they get their shots.
Anyone who gets a COVID-19 vaccine can sign up for v-safe here.
Correction April 7, 1:20PM ET: V-safe does collect severity information, though this wasn’t reported in the JAMA study. An earlier version of this story erroneously said that v-safe did not collect this information. We regret the error.