The coronavirus mortality rate might be lower than previously thought, according to a new study.
A group of researchers analyzed data from China and found that the overall mortality rate of COVID-19 was 1.38%. But if they adjusted for cases that likely went unaccounted for due to their mild or asymptomatic nature, the overall mortality rate decreased to around 0.66%, they reported on March 30 in journal The Lancet Infectious Diseases.
Past estimates had placed the mortality rate somewhere between 2% and 3.4% in Wuhan, China where the outbreak first began, according to a previous Live Science report. A recent study published in the journal Nature Medicine had found that the death rate in the city — without including those who were likely asymptomatic — was around 1.4%.
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In this new study, to figure out the true "infection fatality ratio" — the mortality rate that includes the people with mild cases who may have not been counted before — the researchers looked to data from people who were flown back to their various countries from Wuhan, China during the outbreak.
Those repatriated people were given PCR tests — tests which detect specific genetic material within the virus, according to a previous Live Science report. They also used data from Diamond Princess cruise ship passengers who also received PCR testing. Since these tests were given to people who didn't necessarily show symptoms, the researchers were able to estimate the prevalence of such cases.
Consistent with previous research, the new study also found that the death rate varied greatly by age. While the death rate was around 0.0016% in 0 to 9-year-olds, it increased to about 7.8% for people who were age 80 and above.
The researchers also found that nearly 1 in 5 people over the age of 80 infected with COVID-19 were likely to require hospitalization whereas only 1% of people under 30 were likely to be hospitalized.
"Estimating the case fatality ratio for COVID-19 in real time during its epidemic is very challenging," Shigui Ruan, a professor in the department of mathematics at The University of Miami wrote in an accompanying commentary. But the infection fatality ratio "is a very important piece of data that will help to guide the response from various government and public health authorities worldwide."
The case fatality ratios will vary slightly from county to country, based on differences in the policies and measures put in place to control the outbreak, he added. In any case, these mortality rate estimates are still much higher than that of the seasonal flu, which kills around 0.1% of people who are infected.
"Even though the fatality rate is low for younger people, it is very clear that any suggestion of COVID-19 being just like influenza is false," he wrote. For those between the ages of 20 to 29, for instance, the chance of dying from SARS-CoV-2 is 33 times higher than the odds of dying from seasonal influenza, he wrote.
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Originally published on Live Science.