How deadly is the new coronavirus? Research so far suggests the fatality rate could be low.

More people in mainland China have now died from the coronavirus outbreak that started in December than from the eight-month SARS outbreak in the early 2000s.

That SARS outbreak was considered the first pandemic of the 21st century, since it spread across 29 countries. In total, 8,000 cases were recorded and 774 people died.

The new coronavirus has killed more than 630 people, infected more than 31,000, and spread across 26 countries. But it appears to be far less deadly than the SARS coronavirus. Whereas SARS had a fatality rate of 9.6% (meaning that nearly 10% of people who caught the disease died from it), the new coronavirus seems to have a fatality rate of around 2% so far, according to the World Health Organization (WHO).

That number could change as more cases come to light, however. As late as last week, The New York Times reported that doctors in Wuhan the city where the outbreak started were still running short on test kits , which leads to delayed diagnoses. After a person has been tested, it takes about one to two days for the results to come back.

Combined, these factors create a lag time between when people are infected and when cases are confirmed.

"My guess is there's a delay in a lot of the reporting," Aaron Milstone, an epidemiologist at Johns Hopkins University, told Business Insider. "If people are sick and they're not getting tested, then we don't know about them."

The real fatality rate could be lower

The virus' fatality rate looks different depending on how you slice it. Most of the cases so far are concentrated in China's Hubei province. The fatality rate there is slightly higher than the global figure: around 2.8%. The rate in Wuhan is even higher: 4.1%.

A study published recently in the Lancet found a fatality rate of 11% among 99 novel coronavirus patients with a history of exposure to the seafood market where the virus likely originated.

But many unknowns remain: Around 1,500 coronavirus patients are confirmed to be in recovery worldwide, which means there are around 29,000 whose fate is uncertain.

hospital wuhan STR/AFP/Getty Images

The virus is also continuing to spread.A peer-reviewed study published in The Lancet recently estimated that an infected person could pass the virus to two to three others, on average. That would mean the infected population could double every 6.4 days. The authors estimated that the true number of cases in Wuhan alone was around 75,800 as of January 25.

But not all infected patients will die, of course. In fact, some health experts predict that the fatality rate could decrease as the number of cases rises.

According to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, cases being reported right now mainly represent people who are going to hospitals with severe symptoms.

"There's another whole cohort that is either asymptomatic or minimally symptomatic," Fauci said at a live briefing from the Journal of the American Medical Association. "We're going to see a diminution in the overall death rate."

The virus could resemble a pandemic flu

Estimates of the coronavirus' incubation period suggest it can last up to 14 days. During that time, carriers can be infectious even when they don't display symptoms. Patients with the virus generally have a fever and respiratory issues like coughing or difficulty breathing.

The current test for the virus can only identify a case when a person is symptomatic.

"We've seen people who had a detectable virus, then they didn't have a detectable virus, and then three days later they had a detectable virus," Robert Redfield, the director of the Centers for Disease Control and Prevention (CDC), said in a briefing last week. "We don't know the natural history of how this virus is secreted."

French lab scientists in hazmat gear inserting liquid in test tube manipulate potentially infected patient samples at Pasteur Institute in Paris, Thursday, Feb. 6, 2020. Scientists at the Pasteur Institute developed and shared a quick test for the new virus that is spreading worldwide, and are using genetic information about the coronavirus to develop a potential vaccine and treatments. (AP Photo/Francois Mori) ASSOCIATED PRESS

Thus far, the majority of people who have died have been elderly patients or those with preexisting health problems. A recent JAMA study of found that the median age of a novel coronavirus patient is between 49 and 56 years old. But Chinese authorities have reported that 80% of the cases in China are among those ages 60 and older.

The WHO reports that 14% of reported cases in China are "severe."

A study published in the New England Journal of Medicine in January also speculated that "children might be less likely to become infected or, if infected, may show milder symptoms" than adults.

Fauci said the new coronavirus could wind up looking more like a pandemic flu than like SARS in terms of its fatality rate. SARS and the new coronavirus share around 80% of their genetic codes , but the virus family also includes pneumonia and the common cold.

The worst pandemic flu, the 1918 Spanish influenza, had about the same fatality rate as the coronavirus right now. But other pandemic flues have been less deadly, Fauci said, with fatality rates between 0.8% and 1.2%.

The normal seasonal flu, he added, has a fatality rate of around 0.1%. This year's strain is even less deadly so far, with a fatality rate of 0.05%, according to the CDC.

"What we're seeing now in terms of illness and deaths reflect people who started getting sick a week ago," David Weber, a professor of epidemiology at the University of North Carolina at Chapel Hill, told Business Insider. "My guess is things will change over time."

Read more about the coronavirus:

Everything we know about the Wuhan coronavirus outbreak

The genetic code of the Wuhan coronavirus shows it's 80% similar to SARS. New research suggests a potential way to neutralize the virus.

Cruise ships, detention centers, seaside resorts, and motels: Photos show how travelers are being quarantined due to the coronavirus

Whistleblower doctor Li Wenliang, who was censored after sounding the alarm about the coronavirus, has died in Wuhan

How deadly is the new coronavirus? Research so far suggests the fatality rate could be low.

The real fatality rate could be lower

The virus could resemble a pandemic flu

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