Infectious Disease

No association between mRNA COVID-19 vaccines and serious side effects

September 03, 2021

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Disclosure:
Blumenthal reports that outside of the study, he has received royalties from UpToDate and grants from the Agency for Healthcare Research and Quality, Massachusetts General Hospital, and the NIH. Klein reports that while conducting the study he received grants from the CDC and outside of the study grants from GlaxoSmithKline, Merck, Pfizer, Protein Science (now SP), and Sanofi Pasteur. Please refer to the study and the accompanying editorial for all relevant financial information from the other authors.

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An interim analysis of 6.2 million people who received more than 11.8 million doses of the mRNA COVID-19 vaccines found no significant association between the vaccines and serious side effects, according to researchers.

“These results of our security monitoring 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 between five Kaiser Permanente service regions, along with the 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% modern; 6,175,813 first cans and 5,669,315 second cans).

The mean age of vaccine recipients was 49 years; about 16% were 65 years or older and 20% were younger than 18 years. 54 percent were female. Most of the vaccine recipients were non-Hispanic White and aged 18 to 49 years. Although the recipients are observed for at least 2 years, only data from December 14, 2020 to June 26, 2021 were included in the current study.

The results published in JAMA showed that the risk comparison intervals for the incidence of ischemic stroke were 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 cans.

Across the cohort as a whole, “the event rates for 23 serious health outcomes were not significantly higher in people 1 to 21 days after vaccination than in similar people 22 to 42 days after vaccination,” wrote Klein and colleagues. “For the less common results, the CIs were wide.”

According to a press release, the researchers also identified 34 cases of myocarditis and pericarditis in recipients of mRNA COVID-19 vaccines aged 12 to 39 years. Of these cases, 85% occurred in men and 82% required a median of 1 day hospitalization and “almost all recovered” at the time of analysis. As a result, the researchers found that for the first week after vaccination, vaccine recipients aged 12 to 39 years were at risk of 6.3 additional cases of myocarditis per 1 million doses.

Klein and colleagues wrote that the limitations of their study included the limited results from COVID-19 vaccines; the possibility that vaccine recipients could not see a doctor because of less serious adverse events; and a short follow-up period.

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

Blumenthal and colleagues added that Klein and colleagues’ results suggest that “mRNA COVID-19 vaccines were safe for the general population”.

Such data is “essential to robust vaccine safety assessments, to educate the public and to overcome vaccine hesitation, especially in pandemic situations where large-scale vaccination is critical and large numbers of people are exposed to new vaccines,” wrote Blumenthal et al Colleagues.

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.

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