Here’s why ‘milder’ omicron caused more deaths in Mass. than delta

“Let’s not keep getting fooled by this virus.”

A syringe is prepared with the Pfizer COVID-19 vaccine at a vaccination clinic at the Keystone First Wellness Center in Chester, Pa., Dec. 15, 2021. Matt Rourke/AP Photo, File

During the eight weeks that omicron was the dominant COVID-19 variant, more excess deaths occurred in Massachusetts than during the entire 23 weeks that delta was driving infections, according to a new study from a group of local experts. 

The levels of excess death — the measure of how many more deaths occurred than would normally be predicted — indicate that despite omicron’s reputation as being more mild for many people, the variant still wreaked havoc in the state. 

During the almost six-month-long delta variant period, 1,975 all-cause excess deaths occurred, as compared to 2,294 excess deaths in the two months when omicron was dominant, the study published Friday in the Journal of the American Medical Association found. 


The high number of excess deaths from omicron is likely attributable to how contagious the variant is, Dr. Jeremy Faust, one of the study’s co-authors and an emergency physician at Brigham and Women’s Hospital, told

Faust and his team used the term “mortality product” to describe how fatality rate and case numbers combine to overall deaths. At its core, mortality product is the idea that overall mortality is the result of multiplying the infection fatality rate and higher infection rate.

“It’s kind of like an old math problem, like one times 10 is the same as two times five,” Faust said. “But when the original strain was two times five [and] now, the new one is one times 50, it’s like ‘wait a minute, that’s more people.’”  

In this situation, the individual case mortality of omicron may have been lower, but there were just so many more cases that the total numbers rose. 

“The reason we care about it is that if it all happens at once in a very short amount of time, which is what happened in omicron, then the stress on the healthcare system is just much much harder to compensate for and to adjust to,” Faust said. “We saw this across the country; hospitals were just like stretched beyond their limits. And that’s terrible for everyone.”


The increase in excess death was largest for older people, but, according to the study, it affected every age range. 

The combination of a much higher number of cases and an overwhelmed medical system resulted in the loss of thousands of lives, Faust said. 

He said one portion of the puzzle that may explain the study’s finding is that, on the whole, Massachusetts fared pretty well against the delta wave, with cases only rising dramatically at the end of the surge.

“Generalizing, ironically states like Massachusetts and New York that did better with delta will have had a worse omicron comparatively, as opposed to places that kind of failed both times — and those places often were the places that have lower vaccination rates,” Faust said.

Places like Florida had really high case counts with both waves, so it’s possible omicron didn’t lead to the same excess death there, Faust said.

In an Inside Medicine post about the study, Faust said he and his colleagues also found (but did not publish in the study) that excess mortality was very related to vaccination rates. In counties with the lowest vaccination rates, more excess mortality occurred. 


“Vaccination is by far the most, in my view, the thing that is most correlated to better outcomes,” Faust said. 

As for what the study tells us about future variants, Faust said it is a cautionary tale. 

Future variants will likely be more contagious and may appear milder, but that is not reason enough to drop our guard, the doctor said.

“Omicron was not mild, and we shouldn’t let future variants fool us,” Faust said. “We now have the ability, through testing the wastewater, to really track these outbreaks. And that means that we can really tailor our responses and put on the mask and decrease capacity of indoor gatherings — just when we have to. And we should, because if we had done that during omicron, we could have saved thousands of lives.”

Faust said a threat assessment with each new variant, combined with quick action, is key to prevent deaths in future waves. 

“As the population gains immunity, it may appear that some people have milder illnesses with each new variant,” he wrote on Inside Medicine. “That is an illusion. Too many people appear to have fallen for that mirage during omicron; it did find and kill an alarming number of people. Excess mortality helps us track that. Let’s not keep getting fooled by this virus.”


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