COVID-19 May Have Arrived in US in December: Study

Of 90 samples the researchers could perform follow-up tests on, 84 showed some evidence of antibodies blocking SARS-CoV-2 from binding to ACE2, a receptor the coronavirus uses to enter host cells.

Positive SARS-CoV-2 antibody tests suggest a prior COVID-19 infection, but they do not provide definitive proof, as prior exposure to other coronaviruses—some of which can cause a common cold—can produce a false-positive result. The authors conclude that it is unlikely that all 84 samples represent false positives, and therefore at least some reflect COVID-19 infections in December or early January.

Even though the authors tried to measure antibodies that were specific to SARS-CoV-2, cross-reactivity with other coronaviruses can’t be ruled out, George Rutherford, an epidemiologist at the University of California, San Francisco, who was not affiliated with the study, tells Live Science. He also notes that even if these results show actual COVID-19 infections, the researchers cannot determine where the participants acquired the infection—some blood donors could have recently traveled to China and became infected there, for example.

University of Washington epidemiologist Trevor Bedford, who has been using genetics to understand the timing and location of SARS-CoV-2 spread and was not involved in the study, writes in a Twitter thread that seasonal coronaviruses tend to circulate more often in the winter. He adds that antibody concentrations are typically higher in those recently infected compared to random healthy adults, suggesting that there could be a high false positive rate. Even if the results are accurate, then by extrapolation that would mean there were millions of infections in the general US population, which would have been accompanied by a higher excess death rate, he writes, something that wasn’t observed until March.

To better understand how often false positives occur, the researchers will look at blood samples from prior years to see whether they, as expected, would not show antibodies for SARS-CoV-2, Stramer tells the Times.

“We’re looking at the echoes of somebody’s infection,” Johns Hopkins Center for Health Security immunologist Gigi Gronvall, who was not affiliated with the study, tells USA Today. “I think we have pretty high expectations for the immediacy of our data and . . . the origin of diseases tends to be more murky and require months and years of investigation.”