As the coronavirus spreads, scientists are learning more about the disease’s fatality rate.
The medical journal JAMA released a paper this week analyzing data from the Chinese Center for Disease Control and Prevention on 72,314 coronavirus cases in mainland China, the figure as of Feb. 11, the largest such sample in a study of this kind.
The sample’s overall case-fatality rate was 2.3%, higher than World Health Organization official 0.7% rate. No deaths occurred in those aged 9 years and younger, but cases in those aged 70 to 79 years had an 8% fatality rate and those aged 80 years and older had a fatality rate of 14.8%.
No deaths were reported among mild and severe cases. The fatality rate was 49% among critical cases, and elevated among those with preexisting conditions: 10.5% for people with cardiovascular disease, 7.3% for diabetes, 6.3% for chronic respiratory disease, 6% for hypertension, and 5.6% for cancer.
The fatality rate was 49% among critical cases and worsened by those with preexisting conditions.
The latest China-based study, which was not peer-reviewed by U.S. scientists, found that men had a fatality rate of 2.8% versus 1.7% for women. Some doctors have said that women may have a stronger immune system as a genetic advantage to help babies during pregnancy.
The Chinese study is likely not representative of what might happen if the global spread of the virus worsens. In China, nearly half of men smoke cigarettes compared to roughly 2% of women, which could be one reason for the higher death rate among males.
There are now 81,191 confirmed cases of COVID-19 and at least 2,768 deaths, according to a tally published by the Johns Hopkins Whiting School of Engineering’s Centers for Systems Science and Engineering. (As of Wednesday morning, WHO’s COVID-19 case dashboard, which had been regularly updated, was not working.)
The coronavirus has proven to be more deadly than the SARS virus, but the fatality rate of the coronavirus is still a fraction of that of Severe Acute Respiratory Syndrome (9.6%) and Middle East respiratory syndrome (34.4%). If people die from an illness sooner, they are less likely to be working, shopping or flying on airplanes and, thus, less likely to spread the virus.
“COVID-19 rapidly spread from a single city to the entire country in just 30 days,” the JAMA paper added. “The sheer speed of both the geographical expansion and the sudden increase in numbers of cases surprised and quickly overwhelmed health and public-health services in China.”
The World Health Organization said on Monday that the fatality rate in Wuhan, China, considered the epicenter of the outbreak, is between 2% and 4%. Outside of Wuhan, it is thought to be 0.7%. (Severe acute respiratory syndrome (SARS) had a fatality rate of 9.6%.)
The majority of illnesses and deaths are in Hubei Province where Wuhan — believed to be the epicenter of the outbreak — is located. The illness has now spread to around 40 countries or territories. (WHO has declared a global health emergency.)
While the outbreak has largely affected China — China’s Hubei Province has reported 94% of total deaths and mainland China has 96% of total cases — the emergence of COVID-19 clusters in these other countries has spooked markets this week, Johns Hopkins said.
Coronavirus has an incubation period of up to two weeks, helping the virus to spread. A previous study published in JAMA suggests some patients may be more contagious than others. One patient spread the virus to at least 10 health-care workers and four patients at a hospital in Wuhan.
‘The sheer speed of both the geographical expansion and the sudden increase in numbers of cases surprised and quickly overwhelmed health and public-health services in China.’
“In this single-center case series of 138 hospitalized patients with confirmed novel coronavirus–infected pneumonia in Wuhan, China, presumed hospital-related transmission of 2019-nCoV was suspected in 41% of patients, 26% of patients received ICU care, and [the] mortality was 4.3%.”
SARS had a fatality rate of 9.6%. “The incubation period for SARS is typically 2 to 7 days, although in some cases it may be as long as 10 days,” the CDC said at the time. “In a very small proportion of cases, incubation periods of up to 14 days have been reported.”
Maciej Boni, an associate professor of biology, at Pennsylvania State University, wrote in the online science magazine LiveScience that the 2009 H1N1 flu pandemic initially overestimated the final fatality rate, while the SARS fatality rate rose as the virus spread.
Initially, scientists estimated a fatality rate of 7%. “However, the initially reported information of 850 cases was a gross underestimate,” Boni wrote. “This was simply due to a much larger number of mild cases that did not report to any health system and were not counted.”
“After several months — when pandemic data had been collected from many countries experiencing an epidemic wave — the 2009 influenza turned out to be much milder than was thought in the initial weeks. Its case fatality was lower than 0.1% and in line with other known human influenza viruses.”
“Every now and then a disease becomes so dangerous that it kills the host,” Matan Shelomi, an entomologist and assistant professor at National Taiwan University, wrote on Quora in 2017. But, ideally for the host at least, it must strike a balance.
“If the disease is able to spread to another host before the first host dies, then it is not too lethal to exist. Evolution cannot make it less lethal so long as it can still spread,” he added. “If a hypothetical disease eradicates its only host, both will indeed go extinct.”