NIH researchers find more evidence Covid was circulating in the US in December 2019 Researchers have found more evidence that coronavirus was circulating at low levels across the United States as early as December 2019 -- weeks before the fi... Posted: Jun 15, 2021 4:34 PM Updated: Jun 15, 2021 4:50 PM Posted By: CNN Researchers have found more evidence that coronavirus was circulating at low levels across the United States as early as December 2019 -- weeks before the first officially reported cases. Frozen blood samples indicate people in five states -- Illinois, Wisconsin, Pennsylvania, Mississippi and Massachusetts -- were infected with coronavirus days or weeks before any cases were officially reported in those states.