man's hand in hospital bed

Most people who catch the new coronavirus SARS-CoV-2 recover at home, and some need hospitalization to fight the virus. But in a number of patients, the disease called 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 Tuesday (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%. In Italy, where the death toll from the virus stood at 52 as of March 4, the fatalities were all in people over age 60.

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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.

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.

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.

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.

In South Korea, the outbreak of coronavirus among members of the Shincheonji Church of Jesus is beginning to provide new data on transmission, severity and mortality, Marc Lipsitch, the director of the center for communicable disease dynamics at the Harvard T.H. Chan School of Public Health said in a forum on Monday (March 2). In South Korea, as of March 4, 5,186 cases have been diagnosed and 28 have died. However, he said, those data are still preliminary and hard to interpret. In the United States, testing for coronavirus is still too inadequate to provide any firm numbers, he added. Thus, any calculations of mortality rate should be taken with a grain of salt.

“All of those numbers are very much in flux, and very speculative,” Lipsitch said.

Coronavirus basics

The novel coronavirus, now called SARS-CoV-2, causes the disease COVID-19. The virus was first identified in Wuhan, China, on Dec. 31, 2019. Since then, it has spread to every continent except Antarctica. The death rate appears to be higher than that of the seasonal flu, but it also varies by location as well as a person’s age, underlying health conditions, among other factors. 

Scientists aren’t certain where the virus originated, though they know that coronaviruses (which also include SARS and MERS) are passed between animals and humans. Research comparing the genetic sequence of SARS-CoV-2 with a viral database suggests it originated in bats. Since no bats were sold at the seafood market in Wuhan at the disease’s epicenter, researchers suggest an intermediate animal, possibly the pangolin (an endangered mammal) is responsible for the transmission to humans. There are currently no treatments for the disease, but labs are working on various types of treatments, including a vaccine. 

Originally published in Live Science.

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