Less severe course of COVID-19 is associated with elevated levels of antibodies against seasonal human coronaviruses OC43 and HKU1 (HCoV OC43, HCoV HKU1).

The clinical course of COVID-19 is very heterogeneous: most infected individuals can be managed in an outpatient setting, but a substantial proportion of patients requires intensive care, resulting in a high rate of fatalities. We performed a biomarker study to assess the impact of prior infections with seasonal coronaviruses on COVID-19 severity. Sixty patients with confirmed COVID-19 infections were included (age 30-82; 52 males, 8 females): 19 inpatients with critical disease, 16 inpatients with severe or moderate disease, and 25 outpatients. Patients with critical disease had significantly lower levels of anti-HCoV OC43-NP (P = 0.016) and HCoV HKU1-NP (P = 0.023) antibodies at the first encounter compared to other COVID-19 patients. Our results indicate that prior infections with seasonal coronaviruses might protect against a severe course of disease.