New study of 6.2 million patients shows mRNA COVID-19 vaccines are safe

The study, published in JAMA and co-authored by HealthPartners Institute researcher, validates existing safety data and provides reassurance to those who may be hesitant to get vaccinated against the virus.

Bloomington, Minn. — A new study of 6.2 million patients found that no serious health effects could be linked to the two mRNA vaccines currently being used to protect against COVID-19.

The study, which was published in JAMA and involved HealthPartners Institute, compared health events within 3 weeks of each patients’ mRNA vaccinations to health events that occurred 3 to 6 weeks after each patients’ mRNA vaccinations. Researchers looked at 23 potential side effects that were monitored during the vaccine clinical trials and reported among those who received the vaccines after authorization.

These potential side effects included neurological disorders such as encephalitis/myelitis, seizures, and Guillain-Barre syndrome; cardiovascular problems such as acute myocardial infarction, stroke, and pulmonary embolism; and others such as Bell’s palsy, appendicitis, anaphylaxis, and multisystem inflammatory syndrome.

After identifying potential side effects and conducting complex statistical analyses, the researchers concluded that neither mRNA vaccine currently in-use produced any “safety signals,” a phrase used to describe recurring concerns.

“Our data validates the safety profile of these mRNA vaccines,” said Elyse Kharbanda, MD, senior investigator with HealthPartners Institute and co-author on the study. “Vaccines are our best hope for returning to more normal lives. They help prevent COVID-19 and we can feel even more confident that they’re safe.”

Notably, the study identified 34 cases of heart inflammation in patients aged 12 to 39 years. 85% of these cases occurred in males. 82% of these people were hospitalized for a median of 1 day. The authors calculated that among patients aged 12 to 39 years, there is a slight risk of 6.3 additional myocarditis cases per million doses during the first week after vaccination.

However, a separate study recently published in the New England Journal of Medicine shows that heart inflammation events are far more likely after COVID-19 infection than vaccination.

The JAMA study involved eight large health systems, including HealthPartners, that make up the Vaccine Safety Datalink (VSD). VSD is a research network that conducts post-marketing surveillance of vaccines licensed and used in the United States. The other health systems include 5 Kaiser Permanente regions, the Marshfield Clinic, and Denver Health, all in collaboration with the Centers for Disease Control and Prevention, which funded the work.

This study did not analyze the Janssen (Johnson & Johnson) vaccine.