Just how fatal is the coronavirus? Experts are still struggling — months after the virus emerged — to answer that question. Epidemiologists trying to pin down a fatality rate for covid-19 say they simply lack enough reliable data.
On Monday, for example, China’s Center for Disease Control and Prevention published a study with the best and most conclusive statistics. Drawing on the patient records of 44,672 confirmed cases, Chinese researchers deemed the virus to have an overall fatality rate of 2.3 percent.
“The problem is they basically just took the total number of deaths and divided it by number of cases,” said Caitlin Rivers, an epidemiologist at Johns Hopkins Center for Health Security. “It’s not exactly the ideal way to understand fatality rate because it doesn’t take the element of time into consideration.”
The study didn’t take into account, for example, that the virus has a long incubation period, meaning many patients who were recently diagnosed and may go on to die were not recorded as fatalities. That could lead to an underestimation of the virus’s fatality rate.
At the same time, many experts believe the virus’s symptoms are so mild in some people — especially those who are young — that it is going undetected and undiagnosed. That could lead to an overestimation of the fatality rate.
In a Tuesday news conference, WHO officials talked of other barriers to their round-the-clock efforts to understand the coronavirus’s lethality.
Michael Ryan, WHO’s director for health emergencies, noted that while the Chinese CDC study showed a large drop in fatality rate compared with earlier estimates, there was likely “a huge bias at the beginning,” which overestimated its death rate.
“Remember at the beginning of the outbreak what people were finding were the severe cases. … And now, we are going out looking for less sick people,” Ryan said.
He recalled how something similar happened during the H1N1 pandemic when experts initially declared fatality rates of 10-20 percent before lowering them significantly as weeks passed.
Another wrinkle researchers must consider is how much more lethal the virus has proved to be in the epicenter in Hubei Province — 2.9 percent fatality rate — compared with in other Chinese provinces — 0.4 percent.
The sheer number of cases in Wuhan and Hubei province has put enormous pressure on the local health-care system, and some patients may be dying from insufficient health care and resources. Lessons Chinese doctors have learned in Wuhan are also being applied in other Chinese cities as the virus spreads, enabling them to reduce fatalities.
Those caveats aside, experts say, the Chinese CDC study contained critical information for researchers. It confirmed, for instance, a long-held suspicion by researchers that the virus is much more lethal for older people. The fatality rate for those over 80, for example was 14.8 percent. Meanwhile, the study found only eight deaths total since the outbreak began for the ages 0 to 29.
Those with existing medical conditions were also much more likely to die — with heightened fatality rates ranging from 10.5 percent with heart disease and 7.3 percent with diabetes to 5.6 percent for cancer.
One particularly perplexing study finding was a higher mortality rate among men (2.8 percent) than women (1.7 percent). Researchers, however, cautioned that that finding could be because of completely unrelated reasons — such as higher smoking rates among Chinese men, gender differences in immune response or women being more likely to seek medical help.
“But the biggest looming question is still the fatality rate and risk this virus poses,” said Rivers. “Anytime there’s an outbreak like this, we hold our breath a little bit, because it takes a lot of time and data before we will know exactly what we’re dealing with.”