According to this study, tests on blood donated between 12/13/19 - 1/17/20 in 9 states showed SARS-CoV-2 antibody activity. In other words, it looks like the corona virus may have been spreading in the U.S. as early as December 2019.
Retrospective SARS-CoV-2 serological testing of routine blood donations collected in 9 US states from 13 December 2019–17 January 2020 suggests that the vi
academic.oup.com
I'm wondering what they would find if they went back even earlier.
Also, I do not know how precise these antibody tests are, which makes wonder if the results might be due to antibodies for one or more of the corona viruses that cause the common cold. For example, the CDC says that a positive antibody test might be caused by a different virus:
>>>A positive test result shows you may have antibodies from an infection with the virus that causes COVID-19. However, there is a chance that a positive result means you have antibodies from an infection with a different virus from the same family of viruses (called coronaviruses).<<<
Symptoms, testing, what to do if sick, daily activities, and more.
www.cdc.gov
This is not directly on point, but there is evidence that there is some cross reactivity in T cells:
>>>“We have now proven that, in some people, pre-existing T cell memory against common cold coronaviruses can cross-recognize SARS-CoV-2, down to the exact molecular structures,” Weiskopf says. “This could help explain why some people show milder symptoms of disease while others get severely sick.”<<<
Blood samples taken before the COVID-19 pandemic showed that some people already had certain immune cells that recognize SARS-CoV-2, possibly because of common colds.
www.nih.gov
The NIH goes on to say antibodies have
not shown significant cross-reactivity:
>>>Notably, these findings contrast with those from antibodies, which haven’t shown significant cross-reactivity between common cold coronaviruses and SARS-CoV-2. More research is needed to determine whether immune cell cross-reactivity contributes to the wide range of symptoms seen with COVID-19.<<<
On the face of it, this seems somewhat contradictory to the CDC statement (if one assumes that "significant cross-reactivity" is required to test positive for antibodies). The NIH item seems to suggest that the tests run on the donated blood probably were detecting SARS-CoV-2 antibodies, not antibodies to one of the corona viruses that cause the common cold.
Having said that, it's still unclear to me how solid the evidence (antibody tests) using donated blood is with regards to the SARS-CoV-2 virus being present in the U.S. as early as December 2019. I guess it's mostly academic at this point.