Researchers believe they have found evidence that SARS-CoV-2, the virus that causes COVID-19, was circulating in low levels across the US around the 2019-2020 holiday season, weeks before it was first documented by US health authorities.
As reported in the journal Clinical Infectious Diseases, scientists at the National Institutes of Health and Centers for Disease Control and Prevention (CDC) analyzed the blood samples taken between January 2, 2020, and March 18, 2020, from 24,000 people across 50 US states as part of the “All of Us” study.
Within this subnational sample, they discovered IgG antibodies against SARS-CoV-2 using two different serology tests in the blood of nine participants. The earliest positive sample was taken on January 7. Since it takes around two weeks for this type of antibody to emerge, so the researchers believe the person was infected as early as December 24, 2019.
The first officially confirmed case of a COVID-19 infection in the US was on January 20, 2020, after a Chinese national traveled to Snohomish County in Washington State from Wuhan, the city in China where the outbreak was first reported in late December 2019. These new findings suggest this was not actually the first case on US soil.
The study also picked up a number of possible cases that predate the official first cases detected in Illinois, Wisconsin, Pennsylvania, Mississippi, and Massachusetts. Unexpectedly, the researchers didn’t find any possible early cases in New York, Seattle, or any other urban hotspots that were hit hard during the early days of the pandemic.
“Antibody testing of blood samples helps us better understand the spread of SARS-CoV-2 in the US in the early days of the US epidemic, when testing was restricted and public health officials could not see that the virus had already spread outside of recognized initial points of entry,” Keri N Althoff, PhD, lead author and associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore, said in a statement.
Also of note, seven of the nine positive samples were from older minority groups, five of which were Black/African Americans and two Hispanic. This further highlights the now well-established evidence that racial and ethnic minorities are disproportionately affected by COVID-19.
However, there are a few caveats to consider. The problem is false positives, ie the test result wrongly indicating the presence of antibodies. It’s also difficult to discern whether the antibodies were specifically against SARS-CoV-2 or another coronavirus, such as the ones that cause a common cold. While the findings are by no means definitive, it’s not the first piece of research that’s pushed back the timeline of COVID-19.
As it currently stands, the first confirmed case of COVID-19 was reported on December 1, 2019, in an elderly man living in the Chinese city of Wuhan, although there have also been unverified reports suggesting the first infection occurred in November 2019. Scientists have also used molecular clock techniques, which track the history of the virus by looking at its mutation rate, to discover that human-to-human transmission of SARS-CoV-2 may have been occurring as early as mid-October to mid-November of 2019 in China’s Hubei Province.