The analysis was carried out by researchers at the University of Washington's Institute for Health Metrics and Evaluation, who looked at excess mortality between March 2020 and May 3, 2021.
The researchers then compared it with what would be expected in a typical nonpandemic year, and afterwards adjusted those numbers to account for a handful of other pandemic-related factors.
The final count only estimates deaths "caused directly by the SARS-CoV-2 virus," the virus that causes Covid-19, according to the study's authors.
Around the world, the study's authors note, nearly 7 million have died, more than double the reported figure of 3.24 million.
"The analysis just shows how challenging it has been during the pandemic to accurately track the deaths — and actually, transmission — of COVID. And by focusing in on the total COVID death rate, I think we bring to light just how much greater the impact of COVID has been already and may be in the future," said Dr. Christopher Murray, who heads the Institute for Health Metrics and Evaluation.
The researchers at UW ultimately said the extra deaths, which were not directly caused by Covid-19, were effectively offset by the other reductions in death rates, leaving them to attribute all of the net excess deaths to the virus.
"When you put all that together, we conclude that the best way, the closest estimate, for the true COVID death is still excess mortality, because some of those things are on the positive side, other factors are on the negative side," Murray said.
Experts agree that official reports of deaths caused by the disease undercount the true death toll of the virus.
Some countries only report deaths that happen in hospitals, or only when it is confirmed patients have been infected; others have poor health care access altogether.
"We see, for example, that when health systems get hit hard with individuals with COVID, understandably they devote their time to trying to take care of patients," Murray said.
Last month, a group of researchers at Virginia Commonwealth University released a study which examined excess mortality rates in the US through December.
While their study yielded the same results showing the number of excess deaths far exceeded the official death toll, it disagreed that the gap could be blamed entirely on the virus and not other causes.
"Their estimate of excess deaths is enormous and inconsistent with our research and others," said Dr. Steven Woolf, who led the Virginia Commonwealth team. "There are a lot of assumptions and educated guesses built into their model."
Other researchers described the researchers' effort to produce a global model as important.
"We need to better understand the impact of COVID across the globe so that countries can understand the trajectory of the pandemic and figure out where to deploy additional resources, like testing supplies and vaccines to stop the spread," said Jennifer Nuzzo, an epidemiologist at Johns Hopkins.