Re-testing of blood samples has shown that coronavirus may have been circulating in Italy as early as October 2019, two months before China alerted the world to the new disease, researchers have claimed.
The World Health Organization asked for further clarification from researchers at a cancer centre in Milan after they claimed last November that samples from cancer patients showed Covid may have been circulating for several months in northern Italy - even before the first cases were reported in China in November 2019.
“The results of this retesting suggest that what we previously reported in asymptomatic patients is a plausible signal of early circulation of the virus in Italy,” Giovanni Apolone, one of the researchers, told the Financial Times.
“If this is confirmed, this would explain the explosion of symptomatic cases observed in Italy [in 2020]. Sars-Cov-2, or an earlier version, circulated silently, under the surface,” he said.
In the first paper - published last November - researchers tested blood samples from 959 individuals who had been screened for lung cancer and found that 111 tested positive for antibodies against Covid-19.
The earliest sample showing the presence of one type of antibody - IgM - was collected in October 2019, the researchers said.
At the request of the WHO samples were sent for re-testing to VisMederi laboratory in Siena, Italy and Erasmus University in the Netherlands.
The laboratories re-tested 29 of the original samples - some positive and some negative - and 29 control samples from 2018.
According to a new paper published by the Italian researchers, which has not been peer reviewed, three samples were found by both Erasmus and VisMederi to be positive for Covid-type antibodies.
However, Erasmus has a high bar for proof of infection and found that none of the samples contained enough levels of each of the three types of antibodies that it needs to consider proof of infection.
Marion Koopmans, professor of virology at Erasmus, told the Financial Times the results were “interesting”. She said it was “not impossible” that the patients had been infected with Covid.
“Just that you would like to see other pieces of evidence,” she said.
This is not the first time that evidence has pointed to the global circulation of Covid months before the world was first alerted to this new disease.
Studies of routine blood donations suggested the virus was present in the United States as early as December 2019. And a French study found Covid antibodies in serum samples collected in November 2019.
The first cases of Covid were first reported in China in November 2019 but WHO was not informed of a “novel pneumonia” until December 31 that year.
The question of when the virus first emerged - and how soon Chinese authorities were alerted to it - is a key component of investigations into the origins of the disease.
However, Paul Hunter, professor in medicine at the University of East Anglia who was not involved in the research, said these latest results do not provide conclusive evidence.
He said the results should be interpreted with caution as other coronaviruses circulating at the time may have sparked an antibody response.
“This paper is insufficient to prove that the virus was circulating in October. That is not to exclude this as a possibility, just that the paper, though interesting, does not provide sufficient proof,” he said.
“An evolutionary genetics study placed the timing of the first infection somewhere between 6 October 2019 – 11 December 2019 so widespread infection in October is extremely unlikely,” Prof Hunter added.
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