Researchers at INT have reported that retesting of blood samples from late 2019 has again indicated the presence of antibodies normally seen after Covid infection.

The findings appear to show that the virus had spread to Europe from China months earlier than initially thought.

Italy’s – and Europe’s – first Covid-19 patient was officially identified on February 21st, 2020 in Milan’s Lombardy region, which became the epicentre of the outbreak in Europe after the first  ‘native’ cases were detected.

But the study in Milan suggests the virus may have already been circulating in the region for months before that date.

READ ALSO: Coronavirus was spreading in Italy as far back as September 2019, researchers claim

INT researchers recently retested samples after their study last November found that more than 100 people who enrolled in a lung cancer screening trial between September 2019 and March 2020 had antibodies in their blood, indicating that they had already been exposed to the virus without noticing symptoms.

A handful of people had developed antibodies as early as the first week of September 2019, the original research found.

The researchers then tested the samples again looking for coronavirus-linked antibodies, and said they had found traces of infection in three samples after discovering a type of coronavirus-linked antibody, the Financial Times reports.

“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,”

The laboratory retested 29 original Italian samples, some positive and some negative.

The first known coronavirus case was in Wuhan in December 2019, but studies have since detected circulation of the virus in Europe as early as November 2019, including in Milan.

READ ALSO: Coronavirus was already in Italy by December 2019, waste water study shows

In another study, researchers at the University of Milan detected traces of the infection in skin cells from a 25-year-old woman who had a biopsy for an unusual skin condition on November 10th, 2019.

At the time the woman reported having a mild sore throat, and months later tested positive for Covid-19 antibodies in her blood.

Separately, studies of Italian waste water appear to show that the virus was circulating in December in parts of northern Italy.

At the start of the pandemic in February 2020, medical experts in Milan said they believed the virus had already been “circulating unnoticed for weeks” in Italy.