‘Reassuring’: No link between mRNA COVID-19 vaccines and serious side effects

An interim analysis of 6.2 million individuals who received more than 11.8 million doses of the mRNA COVID-19 vaccines revealed no significant link between the vaccines and serious adverse events, according to researchers.

“These results from our safety surveillance are reassuring,” Nicola P. Klein, MD, PhD, director of the Kaiser Permanente Vaccine Study Center, said in a press release.

The researchers analyzed information from the Vaccine Safety Datalink, a collaboration among five Kaiser Permanente service regions, along with Marshfield Clinic in Wisconsin, HealthPartners in Minnesota and Denver Health. The analysis included 11,845,128 doses of mRNA COVID-19 vaccines (57% Pfizer-BioNTech [now branded as Comirnaty], 43% Moderna; 6,175,813 first doses and 5,669,315 second doses).

The mean age of the vaccine recipients was 49 years; about 16% were aged 65 years or older and 20% were younger than 18 years. Fifty-four percent were female. Most vaccine recipients were non-Hispanic white and aged 18 to 49 years. Although the recipients will be followed for at least 2 years, only data from Dec. 14, 2020, to June 26, 2021, were included in the current study.

The results, published in JAMA, showed that the risk vs. comparison intervals for incidence of ischemic stroke was 1,612 vs. 1,781 per 1 million person-years (RR = 0.97; 95% CI, 0.87-1.08); appendicitis was 1,179 vs. 1,345 per 1 million person-years (RR = 0.82; 95% CI, 0.73-0.93); and acute myocardial infarction was 935 vs. 1,030 per 1 million person-years (RR = 1.02; 95% CI, 0.89-1.18). The incidence of confirmed anaphylaxis was 4.8 (95% CI, 3.2-6.9) per 1 million Pfizer-BioNTech doses and 5.1 (95% CI, 3.3-7.6) per 1 million Moderna doses.

Among the entire cohort, “event rates for 23 serious health outcomes were not significantly higher for individuals 1 to 21 days after vaccination compared with similar individuals at 22 to 42 days after vaccination,” Klein and colleagues wrote. “For the less frequent outcomes, CIs were wide.”

According to a press release, the researchers also identified 34 cases of myocarditis and pericarditis in mRNA COVID-19 vaccine recipients aged 12 to 39 years. Of those cases, 85% occurred in males and 82% required hospitalization for a median of 1 day and “nearly all recovered” by the time the analysis occurred. Consequently, the researchers determined that there is a risk for 6.3 additional myocarditis cases per 1 million doses during the first week after vaccination among vaccine recipients aged 12 to 39 years.

Klein and colleagues wrote that limitations to their study included the restricted set of COVID-19 vaccine outcomes; the possibility that vaccine recipients did not seek medical attention for less serious adverse events; and a short follow-up duration.

However, “vaccine adverse event risk is often highest within this short time frame, Kimberly G. Blumenthal, MD, MSc, co-director of the clinical epidemiology program at Massachusetts General Hospital, and colleagues wrote in a related editorial.

Blumenthal and colleagues added that the findings by Klein and colleagues indicate the “mRNA COVID-19 vaccines were safe for the population overall.”

Such data are “essential for robust vaccine safety assessments to inform the public and help overcome vaccine hesitancy, particularly in pandemic situations when large-scale vaccination is critical and very large numbers of individuals are exposed to new vaccines,” Blumenthal and colleagues wrote.

References:

Blumenthal KG, et al. JAMA. 2021;doi.10.1001/jama.2021.14808.

Klein NP, et al. JAMA. 2021;doi:10.1001/jama.2021.15072.