The coronavirus responsible for Covid-19 had been present in the United States since at least December 2019, weeks before the first confirmed case in January 2020, according to a new study published on Tuesday.
The US National Institutes of Health (NIH) analyzed 24,000 blood samples taken from volunteers in the country between January 2 and March 18, 2020.
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Antibodies to the SARS-CoV-2 virus have been detected in nine patients - via two different serological tests to minimize the risk of false positives.
The antibodies sought by these tests (IgG), which
"neutralize"
the ability of the virus to infect cells, do not appear until two weeks after infection.
The first positive samples are from participants in Illinois and Massachusetts, taken on January 7 and 8, 2020, respectively, suggesting that the virus infected them in late December.
These people were therefore neither in New York nor in Seattle, two cities which were considered to be the gateways of the virus.
"Antibody tests allow us to better understand the spread of SARS-CoV-2 in the United States during the early days of the epidemic in the country, when testing was limited,"
said Keri Althoff, professor. associate in epidemiology at Johns Hopkins University, and lead author of the study. This work, published in the journal Clinical Infectious Diseases, corroborates similar results from the Centers for Disease Control and Prevention (CDC), which reached the same conclusion last November.