A study of older adults in the United States led by researchers at Brown University discovered that the risk of adverse effects of both mRNA vaccines is extremely low but is lowest with the Moderna vaccine.
The study author wrote, “While mRNA vaccines against COVID-19 have been found to be safe and effective for the general population, in-depth evidence about safety and effectiveness for older adults and individuals with chronic health conditions is more limited.”
The results of the study were published in the Journal of the American Medical Association Network Open, and the authors compared the risk of adverse events between both mRNA vaccines for COVID-19 (mRNA-1273 and BNT162b2) overall, by frailty level, and by prior history of the adverse events of interest.
This retrospective cohort study was conducted between December 11, 2020, and July 11, 2021, with 28 days of follow-up after the week of vaccination. The researchers used a novel linked database of community pharmacy, and Medicare claims data representing more than 50% of the U.S. Medicare population. The researchers identified community-dwelling, fee-for-service beneficiaries aged 66 years or older who received mRNA-1273 versus BNT162b2 as their first COVID-19 vaccine, and data analysis commenced on October 18, 2022.
Primary outcomes were noted as 12 potential adverse events (e.g., pulmonary embolism, thrombocytopenia purpura, and myocarditis), which were evaluated individually. Employing a claims-based frailty index, the researchers measured frailty, and beneficiaries were classified as nonfrail, prefrail, and frail. The risk of diagnosed COVID-19 was evaluated as a secondary outcome, and generalized linear models projected covariate-adjusted risk ratios and risk differences with 95% CIs.
The study involved 6,388,196 eligible patients with an average age of 76.3 (7.5) years, 59.4% were women, and 86.5% were white. A total of 38.1% of individuals were categorized as prefrail and 6.0% as frail. The risk of all outcomes was low in both vaccine groups.
The researchers found that for older adults in both vaccine groups, the risk of serious adverse events was very low. The researchers also detected that for these older adults, the Moderna vaccine was associated with a 4% lower risk of pulmonary embolism and a 2% lower risk of thromboembolic events. Moreover, the Moderna vaccine was also correlated with a 15% lower risk of being diagnosed with COVID-19 compared with the other available mRNA vaccine.
Lead study author Daniel Harris, an epidemiologist and research scientist in the Center for Gerontology and Healthcare Research at the Brown University School of Public Health, stated, “The results of this study can help public health experts weigh which mRNA vaccine might be preferred for older adults and older subgroups, such as those with increased frailty.”
According to the research team, the enhanced safety of the Moderna vaccine for some adverse events, such as pulmonary embolism, could have been due to its greater protection against COVID-19, especially for nonfrail older adults.
“We think that these two things, safety, and effectiveness, are interrelated,” Dr. Harris said. “The slightly reduced risk of pulmonary embolism and other adverse events that we saw in individuals who received Moderna may be because the Moderna vaccine was also more effective at reducing COVID-19 risk.”
With regard to their findings, the authors wrote, “These findings suggest that compared with BNT162b2, mRNA-1273 was associated with a lower risk of adverse events, possibly due to improved protection against COVID-19.”
Finally, the authors noted that the study could not conclusively decide whether the variations in adverse events were due to safety or effectiveness, and the researchers recommended additional research in this area. They also noted that their study also only explored the first dose of the mRNA vaccines, so another potential next action could entail comparable comparisons for subsequent vaccinations.
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