A doctor at Brigham and Women's Hospital in Boston says data from cruise ship passengers suggests the fatality rate of coronavirus may be lower than expected, but the virus is a potentially devastating one for the old and chronically ill.

Dr. Jeremy Faust, an attending physician in the emergency room and faculty member at Harvard Medical School, reached the conclusion after he reviewed data from the Diamond Princess cruise ship, which was quarantined off the coast of Japan, after more than 700 people contracted the virus in February.

Faust says he took a deep dive on the data because friends and family members kept asking him how deadly the virus is and how worried they should be. After studying the issue, he wrote about it in an opinion piece published in Slate Magazine titled "COVID-19 Isn’t As Deadly As We Think."

Faust first looked at the figures in Wuhan, China at the early days of the outbreak. In China, 25,000 people die per day, but at the zenith of the coronavirus, 25 people per day were dying from the virus, a tiny fraction of daily deaths, he explained.

Then, he studied other epidemics, such as the 2009 H1N1pandemic, where early fatality estimates were 10 times greater than the actual death rate of 1.28 percent. And Faust goes one step further, arguing people shouldn't compare COVID-19 — and the virus that causes the disease — to the Spanish flu of 1918 that killed tens of millions of people. If his hypothesis holds up, the mortality rate for coronavirus will be much lower than the initial 2 to 3 percent that was predicted.

The cruise ship was essentially a floating laboratory, according to Faust. Widespread testing of almost everyone on board, which showed more than half the people infected had no symptoms or were asymptomatic, gave a full picture of the spread of the disease.

The true case fatality rate, known as the CFR, of this virus is likely substantially overstated, Faust said. More testing needs to be done to get an accurate sense of how many more asymptomatic and mild cases there are versus fatalities, he added.

Faust suspects some of the current fatality rate figures will be revised downward especially with more targeted testing of the elderly, who are the most vulnerable to the virus. In a nursing home in Washington state, the virus is wreaking havoc on the frail and has already been blamed for at least 5 deaths.

“The numbers we’ve heard globally are likely to not reflect what we’re going to see once testing captures everybody,” he said.