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Study Finds Side Effects of COVID mRNA Vaccines Mild, Short

March 8, 2022 – Side effects from the Pfizer and Moderna vaccines in the United States have largely been mild and short-lived, a large new study of the first 6 months of vaccinations shows.

Findings of the study, compiled after nearly 300 million doses were administered, were published online in The Lancet Infectious Diseases.

Researchers, led by Hannah G. Rosenblum, MD, CDC’s COVID Response Team, looked at data collected through the Vaccine Adverse Event Reporting System (VAERS) and and a system called v-safe starting in December 2020 through the first 6 months of the US COVID-19 vaccination program.

V-safe is a voluntary, smartphone-based system set up in 2020 specifically for monitoring reactions to COVID-19 and health effects after vaccination.

Of the 298.79 million doses of mRNA vaccines administered in the U.S. during the study period, 340,522 reports were made to VAERS. Of those, 313,499 (92.1%) were considered nonserious; 22,527 (6.6%) were serious, but did not include death; and 4,496 (1.3%) were deaths.

From v-safe reporting, researchers learned that more than half (about 71%) of the 7.9 million participants reported local or systemic reactions, more frequently after dose 2 than after dose 1. Of those reporting reactions after dose 1, about two thirds (68.6%) reported a reaction to one particular area of the body and 52.7% reported a reaction that spread to several places.

Among other findings:

  • Two-thirds of reports involved pain at the injection site after either one or two doses.
  • One third involved fatigue after one dose, while 56% reported fatigue after a second dose.
  • Headaches were reported by 27% after the dose, compared to 46% after the second.
  • Injection site pain, fatigue or headaches usually occurred within the first week after vaccination.
  • In about one third of the reports, patients said they were unable to work or do normal activities after the second dose, while similar reports after the first dose came from 12% of patients.Fewer than 1% of participants needed medical care after dose 1 or 2 of the vaccine.
  • Women were more likely than men to report problems after vaccination, and young people were more likely than those over 65 to experience side effects.
  • While cases of myocarditis and other serious effects were reported, they were rare.

Study authors say these effects were similar to what Pfizer and Moderna reported in clinical trials before they were granted FDA authorization.

‘Robust and Reassuring Data’

"The safety monitoring of the mRNA COVID-19 vaccines stands out as the most comprehensive of any vaccine in U.S. history. The use of these complementary monitoring systems has provided robust and reassuring data," Matthew S. Krantz, MD, and Elizabeth J. Phillips, MD, with the Vanderbilt University School of Medicine in Nashville, said.

Krantz and Phillips point out in a separate commentary that the v-safe reports of reactions are consistent with those reported from clinical trials and a real-life study in the United Kingdom.

"[A]lthough approximately one in 1000 individuals vaccinated may have an adverse effect, most of these are nonserious,” Phillips said in a press release.

There were no unusual patterns, she said.