A study of more than 24,000 stored blood samples representing all 50 states offers evidence that the coronavirus was in five states weeks before the first cases were reported there. Some of the infections were present before the first confirmed case in the country was reported.
The first positive samples came from people in Illinois on Jan. 7, 2020 and in Massachusetts on Jan. 8, 2020. The others were found in Wisconsin (Feb. 3), Pennsylvania (Feb. 15) and Mississippi (March 6), according to the paper published Tuesday in the journal Clinical Infectious Diseases.
The specific antibodies discovered in the blood samples, collected through a National Institutes of Health research program called “All of Us,” don’t appear until about two weeks after a person has been infected, suggesting the coronavirus was present in the U.S. as early as late December.
It’s the most recent study to reveal evidence that COVID-19 was in the U.S. much earlier than initially thought, highlighting the need for early testing as soon as epidemics begin. In the first weeks of 2020, U.S. health officials focused solely on people experiencing coronavirus symptoms who had travel history to Wuhan, China, where the virus first emerged; testing criteria didn’t expand until February.
For reference, the first coronavirus case was confirmed on Jan. 21, 2020 in a Washington resident who had recently traveled to Wuhan.
“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,” study lead author Dr. Keri N. Althoff, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, said in a statement.
The blood samples were collected between Jan. 2 and March 8, 2020, and were analyzed with two different antibody tests that have emergency use authorization by the U.S. Food and Drug Administration. Confirming the findings with two tests instead of one helped minimize false positive results, the researchers said.
Coronavirus antibodies were detected in nine of the 24,000 samples, all of which belonged to people living in areas outside Seattle and New York City, where scientists believed the coronavirus first entered.
For example, a person in Mississippi who had COVID-19 antibodies donated their blood on March 6, but the first confirmed case in that state was reported five days later. In Illinois, a coronavirus antibody positive sample was donated on Jan. 7, yet the first confirmed case didn’t come for another 17 days, meaning the virus may have been in the state as early as Dec. 24, 2019, according to the study.
Seven of the nine people had antibodies prior to the first confirmed case in their state. Five of them were “Black/African Americans” and two “Hispanic, Latino or Spanish,” aligning with current evidence that shows people of color are more vulnerable to infection in the U.S.
The researchers don’t know if the people who had coronavirus antibodies in their blood long before the first reported cases got infected during travel or from their communities.
“Ideally, this study could be replicated in other populations with samples collected in the initial months of the U.S. epidemic and with multiple testing platforms to compare results,” the researchers said.
The study’s data will soon be available to other researchers for follow-up studies to better understand when the coronavirus arrived in the U.S.