Could previous exposure to other coronaviruses offer some protection against SARS-CoV-2?

Talking with vaccine experts for a Knowable story, I keep hearing about the huge gaps in what we know about SARS-CoV-2. It differs from most better-known coronaviruses in many ways, among them its ugly trick of spreading from people showing no symptoms. Scientists are struggling to understand how SARS-CoV-2 immunity works, including the roles of the antibodies targeting the virus that are created by our innate immune system and of the protective cells such as T cells that are activated by the adaptive immune system.

One puzzle is why cases dropped off so quickly in some of the worst-hit areas such as Spain, since studies that measure antibodies to the virus seem to indicate that, even today, relatively low numbers of people have been infected there. That may well be  because in some of those infected the antibodies never hit expected levels and/or don’t last long, worrisome scenarios that get a great deal of attention. Another potential factor, which I first saw courtesy Mayo Clinic’s Vincent Rajkumar, is that exposure to other coronaviruses such as colds might help to defend some of us. This hypothesis is backed up by evidence in Cell, Science Immunology and elsewhere that T cells are already geared up to react specifically to SARS-CoV-2 in some probably small fraction of people who haven’t been exposed to the virus. Even if this hypothesis turns out to hold some truth it should change nothing in our defenses against the pandemic. But let’s hope for a glimmer of light here.