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June 9, 2022


In a recent article in the Boston Globe by Felicia Freyer, “‘Mild’ Omicron variant was highly lethal, the study finds that at least in Massachusetts, an Eastern state of the United States, that the Omicron variant of COVID-19 was not so mild. A recent study of deaths in Massachusetts during Delta and Omicron COVID-19 variant waves shows the opposite to be true, that even the mild Omicron variant appeared to be exceedingly lethal.  The study was conducted by researchers at Brigham and Women’s Hospital in Boston and published in JAMA on May 20, the brief paper tabulated deaths from all causes in Massachusetts during the Delta and Omicron waves. It then compared the number of deaths during each wave with what would be expected in a typical pre-pandemic year.

The definition of “excess deaths” are the number of deaths that exceed what would normally have occurred.  During the period from June 28 through December 5, 2021, when the Delta variant of the coronavirus was dominant, the state of Massachusetts experienced 1,975 excess deaths.  During the time frame from December 27, 2021, through February 20, 2022, when the Omicron variant instead was dominant, there were 2,294 excess deaths.  Quite surprisingly, In other words, in just eight weeks of Omicron being the dominant variant, the state of Massachusetts experienced more excess deaths than in 23 weeks of Delta being the dominant variant.

In their analyses, the authors said that “population covariates” were used to calculate 95% CIs for expected deaths and not clear exactly what this means.  Then they calculated excess mortality for each period which they defined as the difference between the observed deaths and point estimate for sARIMA-determined expected deaths.  The authors did not go into much of any description about the sARIMA method, a type of seasonal time series modeling. Perhaps given the research letter format of their article they were limited on space. Finally they calculated incident rate ratios were calculated to compare the Omicron and Delta periods. According to their result, the per-week Omicron to Delta incident rate ratio for excess mortality was 3.34 (95% CI, 3.14-3.54), which was statistically significant. They say this was statistically significant in all adult age groups at various times in the study period and in each period overall.  Basically, for all adult age groups, the ratio of observed to expected excess mortality increased during the Omicron period compared with the Delta period.  Their conclusions were that from the study findings , the highly contagious (although relatively milder) SARS-CoV-2 variant, Omicron, can quickly confer substantial excess mortality, even in a highly vaccinated and increasingly immune population like people in the state of Massachusetts.  Therefore caution is still advised.


Written by,

Usha Govindarajulu

Keywords: COVID-19, Omicron, Delta, Massachusetts, excess mortality, Brigham & Women’s Hospital


Freyer, Felice J. (May 28, 2022) “‘Mild’ Omicron variant was highly lethal, study finds”

Faust JS, Du C, Liang C, et al. Excess Mortality in Massachusetts During the Delta and Omicron Waves of COVID-19. JAMA. Published online May 20, 2022. doi:10.1001/jama.2022.804.×0/