Study shows slight differences in adverse events from COVID-19 vaccines
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Key takeaways:
- The Moderna COVID-19 vaccine had a slightly lower risk for adverse events vs. the Pfizer vaccine.
- The Moderna vaccine was also linked to greater COVID-19 protection, which may partially explain the findings.
Although both are safe and effective, the Moderna COVID-19 vaccine was linked to greater protection and a slightly lower risk for adverse events compared with the Pfizer-BioNTech vaccine in older adults, data in JAMA Network Open show.
Daniel A. Harris, PhD, a research scientist at Brown University School of Public Health, and colleagues wrote that head-to-head comparisons of the messenger RNA COVID-19 vaccines are necessary for decision-making, but the current evidence is lacking — it does not adequately capture events shortly after vaccination, does not have sufficient adjustment and does not generalize well to older adults.
“Immunization with either mRNA vaccine is substantially better and safer than not being vaccinated at all,” Harris said in a press release. “But in an ideal world where we can have a choice between which vaccine product is used, we wanted to see whether one vaccine was associated with better performance for older adults and those with increased frailty.”
Harris and colleagues conducted a retrospective cohort study to compare the risks for adverse events between BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna).
They used a novel linked database of Medicare and community pharmacy claims and identified 6,388,196 people — 59.4% of whom were women and 86.5% of whom were white — aged 66 years or older who got either Moderna or Pfizer-BioNTech as their first COVID-19 vaccine. The researchers assessed 12 potential adverse events like myocarditis and pulmonary embolism individually and measured frailty with a claims-based frailty index, classifying patients as nonfrail, prefrail and frail.
“Because we had these real-world data and a cohort that included millions of older adults, we were able to tease apart potentially very small differences in vaccine safety and effectiveness and perform analyses on important clinical subgroups,” Harris said in the release.
Harris and colleagues found that the Moderna vaccine was linked to a slightly lower risk for some adverse events than the Pfizer-BioNTech vaccine, potentially because of greater protection against COVID-19.
Specifically, the Moderna vaccine was linked to a lower risk for diagnosed COVID-19 (RR = 0.86; 95% CI, 0.83-0.87). However, this benefit was diminished by frailty level (RR = 0.94; 95% CI, 0.89-0.99).
Additionally, the risk for all outcomes was low in both groups, but adjusted models revealed that the Moderna vaccine was linked to a lower risk of pulmonary embolism (RR = 0.96; 95% CI, 0.93-1) and other events in subgroup analyses. For example, an 11% lower risk for thrombocytopenia purpura among nonfrail participants.
“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,” Harris said in the release.
References:
- Harris DA, et al. JAMA Netw Open. 2023;doi:10.1001/jamanetworkopen.2023.26852.
- Moderna is safest, most effective mRNA vaccine against COVID-19 for older adults, study shows. https://www.eurekalert.org/news-releases/997390. Published Aug. 2, 2023. Accessed Aug. 8, 2023.
Perspective
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This is a very rigorous, large study performed by investigators who are very skilled at doing these large studies. Although there are nuanced differences in the side effects that they discovered between the two vaccines, they are really very, very small differences. From my point of view, clinically, they do not distinguish between the two vaccines in any notable fashion, and I remain very comfortable in recommending the vaccines from both manufacturers, depending upon the availability at the location where the person is seeking to be vaccinated.
Both of these vaccines, as has previously been demonstrated and reinforced by this study, are extraordinarily safe. Both are effective. Primary care physicians need not distinguish between the manufacturers. Get whichever one is available to you. And this has to do with looking forward to the new updated vaccine, which will soon become available we hope in September. Both manufacturers are working on that vaccine. Because we’re now moving away from the pandemic way of delivering vaccines through government supply, they will have to purchase these vaccines, just as they do other vaccines, and my sense is that they can choose whichever vaccine they would like.
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