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A study that put both COVID-19 shots to the test to see which was better for older adults found that the Moderna vaccine was superior.

Of more than 6 million people in the study, the Moderna vaccine had a 4% lower risk for producing pulmonary embolism and a 2% lower risk for clotting. The vaccine also was 15% better at preventing COVID-19 infections compared with the Pfizer vaccine.

The results are only based on the first dose of the mRNA vaccine

The study was published yesterday in JAMA Network Open.

“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,” said Daniel Harris, PhD, lead author, an epidemiologist and research scientist at Brown University’s School of Public Health.

“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,” he added. 

The study was important because it let researchers see how the vaccines performed in more people, Harris said. The average study participant was 76 years old. It is important to look at vaccine effectiveness in older adults, who tend to have more chronic conditions. Also, older adults who live in nursing homes and senior living communities have a higher risk for severe COVID infections.

This risk of experiencing adverse events from the virus is much higher than the risk of adverse events from either vaccine, Harris explained.

“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 said.

In related news, the CEO of Pfizer said that the Food and Drug Administration could give approval to the updated COVID-19 booster by the end of this month. The shot targets the XBB.1.5 subvariant, which began to spread in the winter.