Scientists examined blood samples from US residents, who were collected back in December 2019, and found that some had coronavirus even before China announced its appearance.
As part of the study, experts analyzed more than 7,000 donated blood samples: they were collected by the American Red Cross in nine states from December 13, 2019, to January 17, 2020. Of these, 106 samples tested positive for antibodies against SARS-CoV-2: 39 in California, and 67 in Connecticut, Iowa, Massachusetts, Michigan, Rhode Island, and Wisconsin.
The results of this report suggest that SARS-CoV-2 infection may have been present in the US in December 2019. This is earlier than expected.
Even if we consider the percentage of the likelihood of false-positive tests, it can still be argued that the virus was already in the United States by the beginning of December, scientists say.
According to virologists, the presence of antibodies indicates that the donor had previously contacted the virus. Researchers now plan to contact people who have been found to have antibodies to determine if they were traveling in late 2019 and experienced symptoms similar to COVID-19.
It is noted that the presence of antibodies in a person from the United States may indicate that he recently returned from China. There is evidence that the virus was circulating in China back in November 2019.