The Covid-19 pandemic almost didn’t happen, a new genetic dating study shows

The coronavirus pandemic almost didn’t happen, a new study shows.

Researchers working to show when and how the virus first emerged in China calculate that it probably did not infect the first human being until October 2019 at the very earliest. And their models showed something else: It almost didn’t make it as a pandemic virus.

Only bad luck and the packed conditions of the Huanan seafood market in Wuhan – the place the pandemic appears to have begun – gave the virus the edge it needed to explode around the globe, the researchers reported in the journal Science.

“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 worked on the study, told CNN.

A security personnel checks the temperature of passengers arriving at the Shanghai Pudong International Airport in Shanghai on February 4, 2020. - The new coronavirus that emerged in a Chinese market at the end of last year has killed at least 425 people and spread around the world. The latest figures from China show there are more than 20,400 people infected in the country. Outside mainland China, there have been more than 150 infections reported in around two dozen places. There have also been two deaths, in the Philippines and Hong Kong. (Photo by NOEL CELIS / AFP) (Photo by NOEL CELIS/AFP via Getty Images)

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“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.”

The team employed molecular dating, using the rate of ongoing mutations to calculate how long the virus has been around. They also ran computer models to show when and how it could have spread, and how it did spread.

“Our study was designed to answer the question of how long could SARS-CoV-2 have circulated in China before it was discovered,” said Joel Wertheim, associate professor in the Division of Infectious Diseases and Global Public Health at the University of California, San Diego School of Medicine.

Nancy Pu, a Senior Scientist works in the lab that is focused on fighting COVID-19 at Sorrento Therapeutics in San Diego, California on May 22, 2020. - PCR can make millions of exact copies of a piece of DNA, allowing scientists to extract tiny samples. (Photo by ARIANA DREHSLER/AFP via Getty Images)

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“To answer this question, we combined three important pieces of information: a detailed understanding of how SARS-CoV-2 spread in Wuhan before the lockdown, the genetic diversity of the virus in China and 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.”

The evidence strongly indicates the virus could not have been circulating before that, the researchers said. There have been reports from Italy and other European countries of evidence the virus may have infected people there before October. But Thursday’s study indicates only about a dozen people were infected between October and December, Worobey said.

WUHAN, CHINA - JANUARY 31: (CHINA OUT) Investigative team members of the World Health Organization visit Huanan seafood market in Wuhan on January 31, 2021 in Wuhan, China. With no recorded cases of community transmissions since May 2020, life for residents in Wuhan is gradually returning to normal. (Photo by Getty Images)

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“Given that, it’s hard to reconcile these low levels of virus in China with claims of infections in Europe and the U.S. at the same time,” Wertheim said in a statement. “I am quite skeptical of claims of COVID-19 outside China at that time.”

The study indicates the virus did emerge in China’s Hubei province and not elsewhere, the researchers said.

“Our results also refute claims of large numbers of patients requiring hospitalization due to COVID-19 in Hubei province prior to December 2019,” they wrote.

From a handful of cases “sputtering” along at the end of 2019, the virus exploded around the world. According to Johns Hopkins University, it’s been diagnosed in 121.7 million people and it has killed nearly 2.7 million. The US has been the worst-affected country by far, with close to 30 million diagnosed cases and nearly 540,000 deaths.

The study doesn’t show which animal was the source of the virus. Genetic evidence shows bats carry a closely related virus, and also suggests another, intermediate species of animal was likely infected and transmitted the virus to a human being somewhere.

Members of a World Health Organization team are seen wearing protective gear during a field visit to the Hubei Animal Disease Control and Prevention Center for another day of field visit in Wuhan in central China's Hubei province Tuesday, Feb. 2, 2021. The WHO team is investigating the origins of the coronavirus pandemic has visited two disease control centers in the province. (AP Photo/Ng Han Guan)

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This happens. The US Centers for Disease Control and Prevention regularly tracks and reports on cases of new strains of influenza infecting people who attend county fairs and interact with pigs, for instance. But so far, none of these infections has led to an epidemic or even an outbreak.

What’s needed is an infected person and a lot of contact with other people – such as in a densely packed seafood market. “If the virus isn’t lucky enough to find those circumstances, even a well-adapted virus can blip out of existence,” Worobey said.

“It gives you some perspective – these events are probably happening much more frequently than we realize. They just don’t quite make it and we never hear about them,” Worobey said.

And that could have happened with Covid-19.

In the models the team ran, the virus only takes off about 30% of the time. The rest of the time, the models show it should have gone extinct after infecting a handful of people.

Workers prepare a stall filled with seafood at a market in Beijing on July 10, 2019. - Factory prices in China were unchanged in June from a year ago, data showed on July 10, reviving the prospect of deflation as the US trade war hits the crucial manufacturing sector. At the same time consumer prices managed to meet expectations but the main support came from a surge in food prices owing to the impact of African swine fever on pork supplies and severe weather hitting fresh fruits. (Photo by Nicolas ASFOURI / AFP) (Photo credit should read NICOLAS ASFOURI/AFP via Getty Images)

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“What may have happened here was that the virus was sputtering along in a very low number of people in October, November, into December and then it got into this Huanan seafood market,” Worobey said.

It’s likely the market was not where the virus first infected people, but just the place where it got amplified.

Given how little time the virus was around, it’s remarkable that it was identified so quickly, Worobey said.

“It was pretty clearly some time in December before there were was a sizable enough group of people infected that there was a chance of discovering a new virus,” he said. By January of 2020, it had been sequenced and characterized.

Nonetheless, it was too late – perhaps because Covid-19 isn’t quite deadly enough. The first SARS virus killed close to 10% of its victims in 2002 to 2004 before it was stopped via a concerted global effort.

“As a scientific community, we were certainly aware of the pandemic potential of a highly transmissible, moderately virulent pathogen. But our system of reporting illness is contingent on detecting spikes in hospitalizations and deaths. Clearly that wasn’t enough to stop Covid-19,” Wertheim told CNN.