Antibody testing research suggests COVID-19 may have been circulating in Illinois, Massachusetts, Mississippi, Pennsylvania and Wisconsin before the first official cases were reported there, according to findings published June 15 in Clinical Infectious Diseases.
The study, part of the National Institutes of Health's All of Us Research Program, involved more than 24,000 stored blood samples. Between Jan. 2 and March 18, 2020, researchers tested participants' blood samples using two serology test platforms.
SARS-CoV-2 was detected in nine of the samples. The first positive samples were detected on Jan. 7-8, 2020, from participants in Illinois and Massachusetts, respectively.
This suggests the participants were exposed several weeks earlier in December 2019, given that antibodies typically don't appear until about two weeks after a person is infected, researchers said.
The study authors acknowledged several study limitations, including a low number of samples from certain states, and an inability to determine whether infections were contracted during travel or within participants' own communities.
Some experts told The New York Times the research also did not fully address whether the antibodies were in response to coronaviruses that cause common colds.