Immunity against seasonal human coronavirus OC43 mitigates fatal deterioration of COVID-19

BACKGROUND: The effects of high-intensity immunity on coronavirus disease 2019 (COVID-19) remain unclear. Antibodies against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are preferentially induced in inpatients with COVID-19 compared with outpatients with milder disease, and immunosuppression is the standard therapy for severe cases. This study investigated the relationship between cross-reactive antibody production against seasonal human coronavirus and the clinical course of COVID-19. METHODS: Among the immunogenic epitopes of SARS-CoV-2, conserved peptides in human coronavirus OC43 were searched and synthesized. Enzyme-linked immunosorbent assay was designed to detect antibodies against synthesized peptides. Antibody titres against S2ʹ cleavage site epitopes near fusion peptides of SARS-CoV-2 and OC43 were determined in the sera of 126 inpatients with COVID-19. The correlation between antibody titres and clinical data was analysed. RESULTS: Inpatients with COVID-19 who produced antibodies against OC43 did not develop severe or fatal pneumonia. Antibody titres against the corresponding epitope of SARS-CoV-2 did not differ between inpatients with severe and mild COVID-19. Antibody titres against the OC43 epitope increased more than those against SARS-CoV-2 during the first 2 weeks of COVID-19. CONCLUSIONS: Immunity to seasonal human coronavirus OC43 effectively enhanced recovery from COVID-19. Detecting cross-reactive antibodies to OC43 may help to predict prognosis for patients with COVID-19.