‘What see’st thou else in the dark backward and abysm of time?’ –Shakespeare
By mid-December, the Northern Hemisphere is usually well into the start of its annual cold and flu season — but so far this year, even as the COVID-19 pandemic surges in dozens of countries, the levels of many common seasonal infections remain extremely low. […] In the Southern Hemisphere — now past its winter — seasonal influenza hardly struck at all. That looks as though it might happen in the north, too.
Conversely, some common-cold viruses have thrived, and tantalizing evidence suggests that they might, in some cases, protect against COVID-19. One study of more than 800,000 people, for example, showed that adults who had had cold symptoms within the previous year were less likely to test positive for SARS-CoV-2 — although why this is so remains a mystery. […] One possible explanation is that previous infection with a coronavirus (another cause of the common cold) could confer some immunity to SARS-CoV-2. […] Previous coronavirus infections do seem to generate T cells and B cells — immune-system cells that help to attack and remember pathogens — that can recognize SARS-CoV-2. These pre-existing cells might provide some partial cross-protection against the new coronavirus. A few studies have shown that, because of other coronavirus infections, about one-quarter of people have antibodies that can bind to the SARS-CoV-2 virus. […]
Another way that seasonal colds might be contributing to COVID-19 immunity is that a current rhinovirus infection might interfere directly with SARS-CoV-2 — perhaps by kicking off interferon responses, part of the immune system that inhibits viral reproduction. A study6 by Ware and his colleagues, for example, shows that someone with a rhinovirus infection is 70% less likely to also get a common coronavirus infection, compared with someone who doesn’t have the sniffles.
