Some patients have few or mild symptoms from covid19 infection; and the explanation may include recent infections with similar viruses or recent vaccines, which provided partial protection and mitigated or prevented symptoms. We wonder, however, if some asymptomatic and mildly symptomatic covid19 patients assumed they had allergies, a seasonal cold, ate something to upset their stomach, had a flare-up of an underlying medical problem, etc. They may also have simply forgotten they had these symptoms, by the time they test positive for antibodies to covid-19.