PHOENIX - A study published on March 18 found that the novel coronavirus may have been lingering undetected as early as October 2019, two months before the first reported human case of infection in Wuhan, China in December.
"It is highly probable that SARS-CoV-2 was circulating in Hubei province at low levels in early-November 2019 and possibly as early as October 2019, but not earlier," study authors said.
Researchers at the University of Arizona, University of California San Diego School of Medicine and Illumina, Inc. used molecular dating tools and found that the pandemic might not have happened if not for a few key events.
"It was a perfect storm — we know now that it had to catch a lucky break or two to actually firmly become established," Michael Worobey, a professor of evolutionary biology at the University of Arizona who co-authored the study told CNN.
"If things had been just a tiny bit different if that first person who brought that into the Huanan market had decided to not go that day, or even was too ill to go and just stayed at home, that or other early super-spreading events might not have occurred. We may never have even known about it."
Authors of the March 18 study published in the journal Science noted that their epidemiological simulations found that the coronavirus dies out naturally more than three-quarters of the time.
This combined with their finding that the virus had gone undetected for several months suggests that it could have died out before causing an epidemic, according to researchers.
But the study authors didn’t set out to speculate on "what if’s" with this pandemic. They instead wanted to know "when."
"A lot has been learned over the last year about this pandemic, but one of the most important questions of all has remained unanswered: When exactly did the outbreak begin?" said Worobey.
"Our study was designed to answer the question of how long could SARS-CoV-2 have circulated in China before it was discovered?" added senior author Joel O. Wertheim, associate professor in the Division of Infectious Diseases and Global Public Health at UCSD.
To answer this question, researchers analyzed exactly how SARS-CoV-2 spread in Wuhan before the initial lockdown, the genetic diversity of the virus and the reports of the earliest cases of COVID-19 in China.
"By combining these disparate lines of evidence, we were able to put an upper limit of mid-October 2019 for when SARS-CoV-2 started circulating in Hubei province," Wertheim said.
According to the U.S. Centers for Disease Control and Prevention, coronaviruses come from a large family of viruses. There are actually a variety of previously known human coronaviruses, but the strain of the virus that has now killed millions of people worldwide is new and also known as a zoonotic coronavirus. That means it is believed to have been transmitted from some unknown species of an animal host to humans.
Researchers say the first cluster of cases are associated with a wholesale seafood market in Wuhan, but argue that those first cases of human transmission did not bring about the beginning of the pandemic.
Study authors say some newspaper reports documented possible COVID-19 diagnoses in Hubei, the province where Wuhan is located in China, as early as Nov. 17, 2019.
Using molecular dating, which analyzes the mutation rate of the genes of COVID-19, scientists were able to identify the virus’ common ancestor.
All genetic data for SARS-CoV-2, the virus that causes COVID-19, derives from a common ancestor that contains similar genetic material — genetic material that is also found in other previously identified coronaviruses.
The molecular dating technique used by scientists to determine the most recent common ancestor of the coronavirus helped them determine the index case of the disease or the first documented case of an infectious disease like COVID-19.
"The index case can conceivably predate the common ancestor – so the actual first case of this outbreak may have occurred days, weeks, or even many months before the estimated common ancestor. Determining the length of that 'phylogenetic fuse' was at the heart of our investigation," Worobey explained.
The researchers also used epidemic simulations to determine how COVID-19 spreads and mutates. They found that only 29.7% of simulated epidemics established "self-sustaining epidemics."
"The remaining 70.3% of epidemics went extinct," study authors said.
Researchers say their work highlights the unpredictable dynamics that "characterized the earliest days of the COVID-19 pandemic."
"In addition to clarifying when that first person became infected in China, our work shows just what an immense challenge it is to nip in the bud a pandemic caused by a virus such as SARS-CoV-2," Worobey said. "There would have been so few cases in those early weeks, with a large proportion of those cases not even showing symptoms. We are going to have to up our game dramatically if we hope to block future pandemics like this one."