When did patient zero catch COVID-19?

An international study published in the journal PLOS Pathogens this week suggests the first case of COVID-19 most likely occurred on 17 November 2019 in China.

The researchers used computer simulations previously used to map species heading towards extinction to estimate the earliest cases of COVID-19 in China and some of the first countries to which the virus spread.

They say their simulations suggest the virus likely emerged in China in early October to mid-November 2019, with 17 November the most likely date of origin. It then spread to Japan on 2 January 2020, before reaching Europe and North America in mid-January.

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Dr Abrar Chughtai from UNSW Sydney told the AusSMC the findings are “not surprising”.

“Some other indirect evidence also points towards an early origin of SARS-CoV-2,” he says. “For example, the first case of COVID-19 was reported in the US on 19 January 2020, while the analyses of blood donation samples from American Red Cross showed that the virus was present in the US as early as December 2019.”

But those blood sample analyses may have detected other common coronaviruses, or they could have been false positives, added Chughtai.

ANU’s Professor Peter Collignon told AusSMC he believes the virus originated even earlier than 17 November.

“It was likely circulating in people in Wuhan for some time before then,” he says. “Already, in December 2019, there were over a dozen strains of the virus.

“While COVID-19 was not identified to be in high numbers of people in North America and in Europe until February/March 2020, it was likely present a couple of months earlier and during their winters, when spread occurs more readily.”

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Collignon says a severe case in France identified in late December 2019 suggests the virus was present there since at least mid-December 2019.

“In the USA, it was also likely already present in December 2019,” he says.

Associate Professor Stuart Turville from UNSW Sydney told AusSMC that while computer simulations are based on evidence, they have their limitations.

“Modelling like this is important but always relies on the last known tangible evidence,” he says. “What would be front-page news would be a study that had serum from people in that area that was reactive to SARS-CoV-2 and these samples were well before October.”

“Unfortunately, with the current pressure of the lab-leak hypothesis and the sensitivities in doing this follow-up research in China, it may be some time till we see reports like that.”

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