The first formal acknowledgement of what was to become the COVID-19 pandemic came on Jan. 9, 2020, when the World Health Organization issued a statement about a mysterious new respiratory disease that had rapidly infected several dozen people in Wuhan, China.
It wasn’t until almost two weeks later that the U.S. confirmed its first case of the virus, with the Centers for Disease Control and Prevention (CDC) announcing on Jan. 21 that a Washington state resident had returned from a trip to Wuhan with the coronavirus in tow.
New research from the National Institutes of Health (NIH), however, found that the virus actually made its way to the U.S. well before that—at least as early as the end of December 2019—and that it had reached far beyond the initial hot spots of Washington state and New York City.
The study tested blood that was originally collected for the NIH’s All of Us research program between Jan. 2 and March 18 of 2020 as part of an ongoing effort to catalog the biological data of at least 1 million Americans for a range of precision medicine and population health projects. Researchers then used Quest Diagnostics' laboratories and two of Abbott’s antibody tests to search for any lingering evidence of COVID-19.
Out of more than 24,000 stored samples gathered from all 50 states, NIH researchers found nine that tested positive for coronavirus antibodies.
The earliest hits came from a Jan. 7 sample from Illinois and a Jan. 8 one from Massachusetts; the others were identified in Mississippi, Pennsylvania and Wisconsin.
Because the virus’s antibodies take at least two weeks after infection to appear, these findings suggest COVID-19 was present in at least a handful of states by the last week of December 2019, if not earlier.
The study’s results build on and seemingly confirm the findings of a previous CDC study of archived American Red Cross blood donations that suggested a small number of cases cropped up in Washington, California and Oregon as early as Dec. 13, 2019.
“Antibody testing of blood samples helps us better understand the spread of SARS-CoV-2 in the U.S. in the early days of the U.S. 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,” said Keri Althoff, Ph.D., lead author of the study and associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.
Althoff added, “This study also demonstrates the importance of using multiple serology platforms, as recommended by the CDC.”
Despite this reframing of the U.S.’s experience with the COVID-19 pandemic, the NIH study’s results don’t paint a complete picture of how the coronavirus spread throughout the country in its earliest days. For one thing, the researchers don’t know whether the positive samples came via community transmission or after travel.
Additionally, because the pool of available blood samples was relatively small and wasn’t equally representative of every state, the researchers acknowledged the virus could potentially have made its way to the U.S. even earlier.
Ideally, according to the NIH, the study will be replicated with other samples gathered in late 2019 and early 2020—and validated on multiple platforms—to build a more complete timeline of the spread of the disease.