How deadly is the new coronavirus?

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Editor's note: Updated March 25 with the latest information on COVID-19. 

The death rate from the novel coronavirus that causes the COVID-19 disease varies by location, age of person infected and the presence of underlying health conditions. 

While most people who catch the new coronavirus SARS-CoV-2 recover at home, some may need hospitalization to fight the virus. And in a number of patients, COVID-19 is deadly. 

Scientists can't yet say for sure what the fatality rate of the coronavirus is, because they're not certain how many people have become infected with the disease. But they do have some estimates, and there is a widespread consensus that COVID-19 is most dangerous for elderly patients and those with preexisting health burdens. 

On March 5, Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said during a news conference that about 3.4% of reported COVID-19 patients around the world have died. In a Chinese analysis of more than 72,000 case records, 2.3% of those confirmed or suspected (based on symptoms and exposure) to have the virus died. Patients above 80 years of age had an alarmingly high fatality rate of 14.8%. Patients ages 70 to 79 years had a fatality rate of 8% and those ages 60 to 69 had a fatality rate of 3.6%. (Younger age groups had lower fatality rates; 1.3% for those 50 to 59; 0.4% for the age group 40 to 49; and just 0.2% for people ages 10 to 39.) In Italy, which has a high proportion of residents over age 65, the fatality rate is strikingly high, around 10% as of March 25.

A recent study of COVID-19 cases in the United States estimated a mortality rate of 10% to 27% for those ages 85 and over, 3% to 11% for those ages 65 to 84, 1% to 3% for those ages 55 to 64 and less than 1% for those ages 20 to 54.

These numbers shouldn't be taken as the inevitable toll of the virus, however. The case-fatality rate is determined by dividing the number of deaths by the total number of cases. Epidemiologists believe the total number of infections with SARS-CoV-2 is underestimated because people with few or mild symptoms may never see a doctor. As testing expands and scientists begin using retrospective methods to study who has antibodies to SARS-CoV-2 circulating in their bloodstreams, the total number of confirmed cases will go up and the ratio of deaths to infections will likely drop.

For example, in South Korea, which conducted more than 140,000 tests for COVID-19, officials found a fatality rate of 0.6%.

However, complicating the matter, mortality numbers lag behind infection numbers simply because it takes days to weeks for severely ill people to die of COVID-19. Thus, current death rates should properly be divided by the number of known infections from the previous week or two, researchers wrote in February in Swiss Medical Weekly.

A report published March 13 in the journal Emerging Infectious Diseases adjusted for this "time delay" between hospitalization and death. The authors estimated that, as of Feb. 11, the death rate from COVID-19 was as high as 12% in Wuhan, 4% in Hubei Province and 0.9% in the rest of China.

Another factor affecting the deadliness of the new coronavirus is the quality of medical care. Already, there is evidence that the overwhelmed medical system in Wuhan, where the outbreak began, led to more deaths. The World Health Organization's joint mission report from Feb. 28 found that among 56,000 laboratory-confirmed coronavirus cases, the case-fatality ratio was 3.8%. However, the case-fatality ratio in Wuhan was 5.8%, while the rest of the country — spared the overwhelming bulk of sick patients — saw a rate of 0.7%.

This means fewer people are likely to die if the medical system is prepared to face an influx of coronavirus patients.

Indeed, in the Emerging Infectious Diseases report, the authors said that the high death rate estimates for Wuhan "are probably associated with a breakdown of the healthcare system," which was overwhelmed with cases. The findings indicate that "enhanced public health interventions, including social distancing and movement restrictions, should be implemented to bring the COVID-19 epidemic under control," the authors said.

As the virus has spread into different parts of the world, new data has emerged. The Diamond Princess cruise ship provided a look at an isolated, well-observed population exposed to the new coronavirus. On that cruise ship, 707 people caught the virus and six died, for a case-fatality ratio of 0.8. It takes about six weeks to determine whether someone with COVID-19 will recover or succumb, so the number of deaths from the cruise ship outbreak could still rise. The current ratio tops the seasonal flu case-fatality ratio in the United States of 0.1%, but it is dwarfed by the 10% case-fatality ratio of SARS, another coronavirus that emerged in China in 2002.

However, the Diamond Princess numbers may not be representative of what happens in the rest of the world. Cruise ship passengers skew older than the general population, putting them at risk of more serious complications. On the other hand, because the outbreak on the ship was closely watched, patients had access to quick medical care.

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Stephanie Pappas
Live Science Contributor

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.