Correlations were highest for serum antibody titers between group I strains (HCoV-229E and -NL63 [r ‫؍‬ 0.443; P < 0.0001]) and between group II strains (HCoV-OC43 and -HKU1 [r ‫؍‬ 0.603; P < 0.0001]) and not statistically significant between HCoV-NL63 and -OC43 and between HCoV-NL63 and -HKU1.