On the original study:
"But it's hard to imagine that a substantial fraction of the population was infected with SARS-CoV-2 in September in Italy without a dramatic uptick in pneumonia-like cases then. For instance, in Spain, far less than 10% of the population tested positive for antibodies to SARS-CoV-2 in the summer, despite the fact that 28,000 people had died from COVID-19 up to that point, according to a survey published in August in the journal The Lancet.
"I would be very cautious," about these findings, said Dr. George Rutherford, professor of epidemiology and biostatistics at the University of California, San Francisco, who was also not a part of the study. The results "have to be confirmed with different antibody tests," that look for the prevalence of antibodies that target other parts of the coronavirus.
His previous experience has shown that such antibody tests for the coronavirus' RBD can create a lot of false positives, Rutherford told Live Science. And because this is "such an unexpected finding," it should be confirmed with other antibody tests such as those that look for antibodies against another one of the coronavirus' proteins, an outer coat called a "nucleocapsid," which is also unique to the novel coronavirus, he said.
Still, "it's not totally outside the realm of possibility," that the virus circulated in Italy earlier than thought. because there is a lot of travel back and forth between China and Italy, especially northern Italy, he said. But considering the earliest COVID-19 case in Wuhan was reported to be in November, "it really gives me pause to say let's really make sure we got this right before we try and explain it," Rutherford said.
How early was the coronavirus really circulating in Italy?