Covid-19 was spreading in China before first confirmed cases, new evidence suggests

New evidence from China confirms what epidemiologists have long suspected: The coronavirus likely began to spread unnoticed in the Wuhan area in November 2019, before exploding in several different locations across the city in December.

Chinese authorities have identified 174 confirmed cases of Covid-19 in the city as of December 2019, researchers from the World Health Organization said, enough to suggest that there were many more mild, asymptomatic or not detected than previously thought.

According to information gathered by WHO investigators during the four-week mission to China to examine the origins of the virus, many of the 174 cases had no known link to the market that was initially believed to be the source of the virus. the epidemic. Chinese authorities have refused to provide the WHO team with raw data on these and potential previous cases, team members said.

Examining 13 genetic sequences of the virus as of December, Chinese authorities found similar sequences among those linked to the market, but slight differences between those of people unrelated to it, according to WHO investigators. The two series likely started to diverge between mid-November and early December, but could possibly indicate infections as early as September, said Marion Koopmans, a Dutch virologist on the WHO team.

The World Health Organization mission in Wuhan found that the coronavirus had most likely spread naturally to humans through an animal.

This, and other evidence, suggests the coronavirus may have reached humans in the second half of November or shortly before, she said, sickening too few people to attract attention until which it leads to an explosive epidemic in Wuhan. By December, the virus was spreading much more widely, both among people with a connection to the market, as well as among others unrelated.

“There must have been many, many more cases in December that people didn’t know or recognize,” said Dominic Dwyer, an Australian microbiologist on the WHO team.

Thea Fischer, a Danish epidemiologist on the WHO team, said last week that the virus “was definitely circulating in the population” before the first severe cases diagnosed, which she called “the tip of the iceberg” .

These assessments, offered by six WHO researchers interviewed by the Wall Street Journal, paint a common picture of how the virus took off in Wuhan: circulating at a lower level, unnoticed, in November, laying the groundwork for a much larger outbreak of cases in December. Other places, like New York or northern Italy, saw a similar pattern of hidden clusters smoldering for several weeks before exploding into epidemics.

New Year’s Eve celebrations on December 31, 2019 in New York City, where hidden clusters smoldered for several weeks before exploding into epidemics.


jeenah moon / Reuters

WHO is seeking access to blood samples from the months leading up to December 2019, to test for antibodies. They also want access to raw data on thousands of people who have fallen ill during that time to try to establish the extent of the virus’s spread ahead of the first officially confirmed case, which Chinese authorities say was December 8.

The virus likely first spread to humans between late September and late November 2019, researchers at the University of Cambridge said last year looking at the rate of mutations in the pathogen.

Likewise, a study by the University of Arizona and the University of California at San Diego suggested that infections in Hubei province, of which Wuhan is the capital, may have occurred as early as mid-October 2019. .

Joel Wertheim, an evolutionary biologist at UCSD and author of the study, described the WHO’s finding of widespread dissemination in December 2019 as “very much in line with our model.”

China’s Foreign Ministry and the National Health Commission did not respond to requests for comment.

Wuhan station was packed with passengers on September 30, 2019, ahead of the national day.


Zhao Jun / Zuma Press

The WHO team did not find any evidence of large clusters of cases in or around Wuhan until December 2019.

“I have no doubt that there would have been a few sporadic cases here and there before December,” said Peter Daszak, a member of the WHO team. “But I don’t think this was something that was circulating widely in China until December.”

The Wall Street Journal reported last week that Chinese authorities had identified 92 patients hospitalized between October and December 2019, whose symptoms suggest they may have had Covid-19. None of them tested positive for antibodies, but the WHO team considers these results inconclusive because the tests were carried out more than a year after the disappearance of any possible infection.


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The team is seeking access to data used to identify potential patients among more than 70,000 cases of influenza-like illness, fever or pneumonia identified during this period. In an interview with Science magazine, the team leader, food safety scientist Peter Ben Embarek, suggested using less stringent criteria to identify around 1,000 potential cases of Covid-19.

Last week, Liang Wannian, head of an expert group on Covid-19 for the Chinese National Health Commission, said there was no evidence of the virus spreading around Wuhan until December. 2019. But he agreed that the genetic sequences showed “that a certain diversity of virus was already present in the first phase of the pandemic in Wuhan, suggesting unsampled chains of transmission beyond the Huanan market. “

The WHO findings have sparked new controversy over the origins of the pandemic, with the United States and Britain expressing concern over what they say is a lack of transparency on the part of China.

Viruses that originate from animals, like the coronavirus, jump to humans during “spillover” events that can initially infect one or two people. A new virus does not always immediately spread to other humans; it may take a few tries. Gradually, however, some viruses begin to spread, and cases then multiply depending on the transmissibility of a virus and the length of its incubation period.


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The first scientifically documented case of Covid-19 was symptomatic on December 1, 2019, but Chinese authorities say the first confirmed case fell ill on December 8 and the first with links to the market fell ill on December 12. A doctor who treated the December 1 patient said he was an elderly man who had other chronic conditions and could not speak, and the exact date of the onset of symptoms was unclear as she had been esteemed by relatives.

Researchers at the University of Arizona and UCSD determined that the virus was spreading as early as mid-October, tracing back from early case reports and taking into account patterns of viral spread and mutation.

It’s no surprise that investigators didn’t find large clusters until December 2019, Dr Wertheim said, with fewer than 20 people infected by the end of November, according to his study model. But eventually, the virus began to spread, with cases doubling every four to five days in December, the scientist said. Viruses cannot circulate for long in a population before they diversify genetically, and this likely started happening between mid-November and mid-December, he said.

Write to Betsy McKay at [email protected], Drew Hinshaw at [email protected] and Jeremy Page at [email protected]

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