March 19 (UPI) — The novel coronavirus first reported in the central Chinese city of Wuhan may have infected people as early as mid-October 2019, according to research from a team of U.S. scientists.
Researchers at the University of California-San Diego, the University of Arizona and Illumina Inc. said in a report published Thursday in journal Science that the virus possibly was circulating for at least two months in China before Chinese authorities alerted the World Health Organization on Dec. 31, 2019.
While the WHO has yet to release its official report on the origins of SARS-CoV-2, researchers say molecular clock evolutionary analyses can trace the virus’ first appearance.
The senior author of the study was Joel Wertheim, an associate professor in the Division of Infectious Diseases and Global Public Health at University of California-San Diego School of Medicine.
“We employed a coalescent framework to combine retrospective molecular clock inference with forward epidemiological simulations to determine how long SARS-CoV-2 could have circulated prior to the time of the most recent common ancestor,” the report said.
“Our results define the period between mid-October and mid-November 2019 as the plausible interval when the first case of SARS-CoV-2 emerged in Hubei province,” it added.
A molecular clock is a method that determines the mutation rate of genes to deduce when two or more life forms diverge, according to UC San Diego. In the case of the coronavirus, the common ancestor of all SARS-CoV-2 variants had appeared by November, the report said.
But Michael Worobey at the University of Arizona said the first cases of the disease most likely emerged even before the appearance of a common ancestor.
“The index case can conceivably predate the common ancestor — the actual first case of this outbreak may have occurred days, weeks or even many months before the estimated common ancestor,” said Worobey, a co-author and a professor of ecology and evolutionary biology.
Scientists also used epidemic simulations to understand the early phase of the pandemic.
Experiments showed only 29.7% of simulated epidemics went on to become “self-sustaining epidemics.”
“The remaining 70.3% of epidemics went extinct,” scientists said.