Harvard Medical School Researchers Find Omicron Subvariant Has Lower Mortality Rate than Previous Strains | News

A Harvard-led team of researchers found that the Omicron BA.2 subvariant — the strain of Covid-19 currently dominating the United States — has a lower death rate than previous strains of the virus, according to an article published in the Journal of the American Medical Association last month.

The study, published on October 25, was led by Harvard Medical School instructor Zachary H. Strasser, and included researchers from HMS, Massachusetts General Hospital and Minerva University. The study found that the Omicron BA.2 subvariant had a mortality rate of 0.3 percent — less than half the 0.7 percent mortality rate of the Delta variant.

“The results suggest that the BA.2 lineage has become substantially less severe than that of the original Omicron variant and the Delta variant,” the authors wrote in the paper.

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To compare the mortality rates of different strains of Covid-19, the researchers used entropy balance – a statistical method that allowed the team to control for different patient conditions, such as vaccination or previous infection.

“We want to compare patients treated the same way to really understand the difference in severity,” Strasser said.

The researchers also considered the effects of potential confounding variables — such as patient comorbidities and previous infections — according to Sean N. Murphy, a professor at HMS who co-authored the study.

“People are all vaccinated now, they’ve had previous infections, and we’ve adjusted for all those different factors and treatments,” Murphy said.

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Although the study results indicate a declining pattern in the strength of Covid-19, Strasser said the trajectory of the virus remains unclear.

“We’re just looking at really three strains, but at least among these three strains, the variants seem to be getting weaker,” Strasser said. “But that doesn’t necessarily mean the trend will continue.”

Strasser cautioned against drawing broad conclusions about the virus from this study.

“There might be a tendency to look at this data and say it means Covid is going away or getting less severe, but really it’s just three data points, three variants,” Strasser added. “That’s good news, and hopefully it will continue, but that doesn’t necessarily mean it has to.”

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Strasser said his team hopes to conduct future studies using electronic health record data to examine the long-term effects of Covid-19, particularly on patients suffering from severe cases of the virus.

“One of the advantages of the electronic health record is that you can capture longitudinal data,” he said. “It’s useful when you’re thinking about something like long-term Covid and you want to look at what’s happening to the patient over time.”

“We will focus more on long-term Covid going forward,” Strasser said.


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