They found that blood samples from some noninfected donors—particularly children—contained antibodies that could recognize both SARS-CoV-2, the virus that causes COVID-19, and other common coronaviruses, such as those responsible for the common cold.
To confirm their results, the researchers analyzed more than 300 blood samples collected from 2011 to 2018. While almost all samples had antibodies against coronaviruses that cause the common cold, 16 of 302 adults (5.3%) had antibodies that would recognize SARS-CoV-2—regardless of whether they had recently had a cold. Only 1 of an additional 13 adult blood donors (7.7%) recently infected with other coronaviruses had cross-reactive antibodies. Of samples from 50 pregnant women, 5 (10%) had such antibodies.
In contrast, 21 of 48 children aged 1 to 16 (44%) had cross-reactive antibodies, with those aged 6 to 16 most likely to have them.