As of Oct 5, 2020, our knowledge of SARS-CoV-2 has only had months to accumulate (figure 1). Although researchers understand more about immunity to other human coronaviruses than about immunity to SARS-CoV-2, that knowledge is also sparse. For reasons that are poorly understood, immunity to seasonal human coronaviruses tends to be short in duration, lasting from 80 days to a few years. Reinfections have been documented with three of the four seasonal human coronaviruses (ie, 229E, NL63, and OC43). Reinfection, after documented infection, has been shown in patients with SARS-CoV-2.1 Whether such reinfection represents non-durable protective immunity, different strains of the same virus, or both, is unclear.2