To characterize the antibody response after HBoV infection further, we measured the IgG antibody in 31 pairs of sera samples that were collected from children with ARTIs. All these children were positive for HBoV1 according to PCR analysis. Based on cELISA, the seroprevalences of HBoV1, 2, 3, and 4 in acute-phase sera were 29%, 25.8%, 16.1%, and 0%, respectively. Of the 31 samples, ten (32.3%) showed an IgG seroconversion for HBoV1, eight (25.8%) for HBoV2, two (6.5%) for HBoV3, and none for HBoV4 (Table2). Two pairs of sera showed concurrent seroconversions to HBoV1 and HBoV2, and one pair showed concurrent seroconversions to HBoV1, HBoV2, and HBoV3. In addition, absorbance at 450 nm increasing in the convalescent-phase serum was observed in seven children (22.6%) who were positive for HBoV1 IgG and eight (25.8%) children who were positive for HBoV2 IgG positive at the acute-phase.