Providence, RI—Pharmacists often are asked to advise on which COVID-19 vaccine is better. The answer now is clearer for older adults.

A recent study in the Journal of the American Medical Association Network Open found that those who received the Moderna COVID-19 vaccine had a lower risk of adverse events than the Pfizer-BioNTech version. Both are mRNA vaccines.

Brown University–led researchers posited that improved protection against SARS-CoV-2 was one explanation. The question they sought to answer was whether any safety differences existed between mRNA vaccines for COVID-19. They also assessed whether those differences were affected by frailty levels.

The results of the cohort study of approximately 6.4 million older U.S. adults indicated a 4% lower risk of pulmonary embolism, a 2% lower risk of thromboembolic events, and a 14% lower risk of diagnosed COVID-19 among those who received the mRNA-1273 vaccine compared with the BNT162b2 vaccine.

“Although both vaccines were safe across frailty subgroups, differences were generally greater in individuals without frailty,” the researchers advised.

“Head-to-head safety comparisons of the mRNA vaccines for SARS-CoV-2 are needed for decision making; however, current evidence generalizes poorly to older adults, lacks sufficient adjustment, and inadequately captures events shortly after vaccination,” the researchers pointed out. “Additionally, no studies to date have explored potential variation in comparative vaccine safety across subgroups with frailty or an increased risk of adverse events, information that would be useful for tailoring clinical decisions.”

The research team conducted the retrospective cohort study between December 11, 2020, and July 11, 2021, with 28 days of follow-up following the week of vaccination. Data analyses were initiated on October 18, 2022.

More than 50% of the U.S. Medicare population was included in the research, with information obtained from a linked database of community pharmacy and Medicare claims data. All participants were community-dwelling, fee-for-service beneficiaries aged 66 years or older who received either mRNA-1273 versus BNT162b2 as their first COVID-19 vaccine. Their mean age was 76.3 years; 59.4% were women and 86.5% were white, with 38.1% categorized as prefrail and 6.0% as frail.

The researchers determined that the risk of all outcomes was low in both vaccine groups. In adjusted models, however, the mRNA-1273 vaccine was associated with a lower risk of pulmonary embolism (risk ratio [RR] 0.96; 95% CI, 0.93-1.00 and risk difference 9; 95% CI, 1-16 events per 100,000 persons) and other adverse events in subgroup analyses (e.g., 11.0% lower risk of thrombocytopenia purpura among individuals categorized as nonfrail).

“The mRNA-1273 vaccine was also associated with a lower risk of diagnosed COVID-19 (RR, 0.86 [95% CI, 0.83-0.87]), a benefit that was attenuated by frailty level (frail: RR, 0.94 [95% CI, 0.89-0.99]),” the authors pointed out.

The authors added that the mRNA-1273 vaccine was associated with larger reductions in adverse events overall as well as diagnosed COVID-19 among recipients categorized as nonfrail. “Because frailty is known to attenuate vaccine response, the greater immunogenicity associated with mRNA-1273 may have been diminished in individuals categorized as frail, thereby reducing its degree of differential protection against COVID-19 and its sequelae,” according to the report.

“Regardless of the underlying mechanism, however, the comparative reduction in morbidity associated with mRNA-1273 is notable and may have real benefits at the population level,” the authors wrote. “Nonetheless, studies confirming the extent to which differences in adverse events can be attributed to early effectiveness are needed.”

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.

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