Pre-existing immunity might not be limited to T cells. A preprint published on medRxiv July 23 reports that SARS-CoV-2–reactive antibodies were found in blood samples taken from people in the UK between 2018 and early 2020, before COVID-19 became widespread in the country.

Not only did the authors find that 15 out of 262 people who never had COVID-19 have IgG antibodies reactive with certain SARS-CoV-2 proteins, but further tests showed that these antibodies had a neutralizing effect on the SARS-CoV-2 spike protein, which suggests that they might be able to restrict infection by the virus.

One of the most striking findings was that these antibodies were far more prevalent in children between the ages of 1 and 16 years old. In fact, 60 percent of children had neutralizing IgG antibodies—an order of magnitude greater than the proportion of adults who were found to have the same antibodies. Coauthor Rupert Beale, an immunologist at the Francis Crick Institute in London, remarked on Twitter that this particular result was completely unexpected—“a kind of bombshell,” as he put it.