Our results show that 17.6% of the adults who were positive for IgG against HBoV1, 2, 3, or 4 based on the ELISA results were negative for IgG against all four HBoVs based on the cELISA results. This finding may be due to antibody waning in the individuals with low IgG levels [22] or to low-affinity antibodies [20, 33] .