PTGER4 and COVID-19: Moreover, three sera from COVID-19-affected healthcare workers recognized HCoV-OC43 N peptides: C 13+ and C 21+, which were positive with the N-Ep4 peptide, and C 10+ sample with N-Ep1, N-Ep3, and N-Ep4 peptides, representing 14.3% of subjects (Figure 3b).