To assess the antibody response of HBoV1-4 IgG in children with acute respiratory tract infections, we used cELISA to determine the seroconversion rate of 31 paired sera from children who were positive for HBoV1 according to PCR analysis. We found that the HBoV1-specific seroprevalence was higher in convalescent sera than in acute sera. However, heterotypic seroconversion against HBoV2 and HBoV3 was also observed. Moreover, for some patients who were positive for HBoV1 and HBoV2 IgG at the acute phase, the absorbance value was higher in convalescent sera. These data may suggest the concurrent production of antibodies against HBoV2 and 3 during the infection of HBoV1, as it has been shown that B-cell memory can be boosted either by the homologous virus or by heterologous, yet immunological related virus [20, 34, 35] .