The novel coronavirus was circulating in Italy since September 2019, a new study by the National Cancer Institute (INT) of the Italian city of Milan finds, three months before it was first reported in China.

In December 2019, cases of pneumonia of unknown cause were reported in central China's Wuhan City. The illness was later identified by the World Health Organization (WHO) as COVID-19 caused by the coronavirus SARS-CoV-2.

WHO has said COVID-19 was unknown before the outbreak was reported in Wuhan late last year, but added that the possibility cannot be ruled out that the virus may have silently circulated elsewhere.

On Monday, the WHO said it was reviewing the results from Italy and seeking clarification. They would contact the paper's authors "to discuss and arrange for further analyses of available samples and verification of the neutralization results."

What does the study say?

The new study adds to the possibility that the virus had originated and spread outside China earlier than widely thought.  

Gabriella Sozzi, an INT biologist, told CGTN Europe that while Italy's first coronavirus patient was officially detected on February 21 in the northern region of Lombardy, blood samples taken in September 2019 showed the presence of the antibodies against the Sars-Cov-2 virus.

"What we noticed, and it was unexpected, we found more than 10 percent of the samples presenting antibodies against the COVID-19 virus," said Sozzi. "This finding seems to tell us that the Sars-Cov-2 virus was probably circulating at a low level in Italy before the outbreak that we had in February."

The Italian researchers' findings, published by the INT's scientific magazine Tumori Journal, show that 11.6 percent of the 959 healthy volunteers enrolled in a lung cancer screening trial between September 2019 and March 2020, had developed coronavirus antibodies well before February.

Further tests

A further specific SARS-CoV-2 antibodies test was carried out by the University of Siena for the same research titled "Unexpected detection of SARS-CoV-2 antibodies in the pre-pandemic period in Italy."

"What we noticed, and it was unexpected, we found more than 10 percent of the samples presenting antibodies against the COVID-19 virus," said Sozzi. "This finding seems to tell us that the Sars-Cov-2 virus was probably circulating at a low level in Italy before the outbreak that we had in February."

It showed that four cases dated back to the first week of October were also positive for antibodies neutralizing the virus, meaning they had got infected in September, Giovanni Apolone, a co-author of the study, told Reuters.

"This is the main finding: people with no symptoms not only were positive after the serological tests but had also antibodies able to kill the virus," Apolone said.

"It means that the new coronavirus can circulate among the population for long and with a low rate of lethality not because it is disappearing but only to surge again," he added.

Italian researchers told Reuters in March that they reported a higher than usual number of cases of severe pneumonia and flu in Lombardy in the last quarter of 2019 in a sign that the new coronavirus might have circulated earlier than previously thought.

(With input from agencies)