Certain mutant strains of SARS-CoV-2 are known to spread widely among humans, including the receptor binding domain (RBD) mutant, Y453F, from farmed minks, and the RBD mutant, N501Y, a mutation common to three major SARS-CoV-2 subvariants (B.1.1.7, B.1.351, and B.1.1.248) and omicron type SARS-CoV-2 BQ.1.1 and XBB.1.16 subvariants. We investigated the characteristics of the RBD mutants, Y453F and N501Y, using three-dimensional structural analysis. We also investigated the effect of Y453F, N501Y or the mutants of RBD of omicron type SARS-CoV-2 BQ.1.1 and XBB.1.16 subvariants on neutralizing antibodies in serum derived from individuals including children (aged 5-11 years) inoculated with mRNA based COVID-19 vaccine (BNT162b2: Pfizer/BioNTech) or COVID-19-positive patients or children (aged 5-11 years) after vaccination with BNT162b2. Our results suggest that SARS-CoV-2 subspecies with the RBD mutations Y453F or N501Y partially escaped detection by 4 neutralizing monoclonal antibodies and 21 neutralizing antibodies in serums derived from COVID-19-positive patients. The significantly low antibody titer of children against Omicron type SARS-CoV-2 BQ.1.1 subvariant and XBB.1.16 subvariant in Japan. Infection with SARS-CoV-2 subspecies that causes serious symptoms in humans may spread globally. In particular, since the antibody titer against the omicron type is low in children (aged 5-11 years) who have been vaccinated with conventional vaccines, therefore it is important for children to receive vaccines specific for the omicron type.