Coronavirus pandemic: Wuhan has a lower death rate than previously estimated, say scientists
A new study says that the case fatality rate in the city is around 1.4%, while past studies have estimated the death rate to be between 2% and 3.4%. By comparison, seasonal flu generally kills about 0.1% of those infected
Wuhan, the epicenter of the COVID-19 pandemic, has a lower death rate than previously estimated, according to scientists. While previous estimates have ranged from 2% to 3.4%, the new analysis pegs it at 1.4% among people who had symptoms in Wuhan.
This is, however, still significantly more than the seasonal flu, which kills about 0.1% of the people it infects in the US. According to the World Health Organization (WHO) estimates, the global death rate for COVID-19 stands at 3.4%. The clinical severity of infectious diseases is typically measured in terms of infection fatality risk, symptomatic case fatality risk, and hospitalization fatality risk. A key public health priority during the emergence of a novel pathogen is estimating clinical severity and how fatal the disease can be, say experts.
“One of the most critical clinical and public health questions during the emergence of a completely novel pathogen, especially one that could cause a global pandemic, pertains to the spectrum of illness presentation or severity profile. For the patient and clinician, this affects triage and diagnostic decision-making, especially in settings without ready access to laboratory testing or when surge capacity has been exceeded. It also influences therapeutic choice and prognostic expectations,” says the research team in their findings published in Nature Medicine.
The team includes experts from the WHO Collaborating Centre for Infectious Disease Epidemiology and Control, The University of Hong Kong, China; and Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, US. They explain that for managers of health services, knowing disease severity is critical to planning procurement of supplies, the readiness of human resources, availability of hospital beds, and generally ensuring the sustainability of the health system through the peak and duration of the outbreak.
Accordingly, using public and published information, the team calculated that the overall symptomatic case fatality risk (the probability of dying after developing symptoms) of COVID-19 in Wuhan was 1.4%. “This is substantially lower than both the corresponding crude or naïve confirmed case fatality risk (4.5%) as of February 29,” say experts.
The analysis is based on figures till February 29, when there were 79,394 confirmed cases and 2,838 deaths from COVID-19 in mainland China. Of these, 48,557 cases and 2,169 deaths occurred in Wuhan.
Hubei province and its capital, Wuhan, reported no new infections for the first time on March 18. No new domestically transmitted cases of the novel coronavirus disease were also reported on the Chinese mainland on March 17, says the Chinese National Health Commission. A total of 7,263 patients are now under treatment at hospitals, including 2,314 in severe condition.
The results of the current study show that for those aged less than 30 years, the average fatality rate was 0.3%. It was 0.5% for those in the 30-59 age group, and 2.6% for those 60 years and above.
The researchers also found that compared to those aged 30-59 years, those below 30 years and those above 59 years were 0.16 and 2.0 times more susceptible to symptomatic infection.
“Compared to those aged 30–59 years, those aged below 30 and above 59 years were 0.6 and 5.1 times more likely to die after developing symptoms. The risk of symptomatic infection increased with age (for example, at ~4% per year among adults aged 30–60 years,” says the analysis.
However, despite a lower symptomatic case fatality rate, the experts warn that COVID-19 is likely to infect many more -- given emerging evidence of presymptomatic transmission and growing evidence of extensive community spread in many countries -- thus ultimately causing many more deaths than SARS and MERS.
“Compared with the 1918 and 2009 influenza pandemics, our estimates are intermediate but substantially higher than 2009, which was generally regarded as a low-severity pandemic. We find that symptomatic case fatality risk is highest in the oldest age group. Unlike any previously reported pandemic or seasonal influenza, we find that risk of symptomatic infection also increases with age,” the findings state.
According to the researchers, even under more realistic assumptions, at least one-quarter to one half of the population will very likely become infected, in the absence of drastic control measures or a vaccine. Therefore, the number of severe outcomes or deaths in the population is most strongly dependent on how ill an infected person is likely to become, and this question should be the focus of attention, says the team.
“Considering the totality of the findings, they nevertheless indicate that COVID-19 transmission is difficult to control. With a basic reproductive number of around two, we might expect at least half of the population to be infected, even with aggressive use of community mitigation measures,” say researchers.
The experts suggest that perhaps the most important target of mitigation measures would be to ‘flatten out’ the epidemic curve, reduce the peak demand on healthcare services and buy time for better treatment pathways to be developed.