Neutralization of BQ.1, BQ.1.1, and XBB with RBD-Dimer Vaccines

   This correspondence reports on the neutralization capacity of ZF2001 (homotypic RBD-dimer vaccine), inactivated-virus vaccines, and chimeric RBD-dimer immunogens against emerging SARS-CoV-2 Omicron subvariants. Human serum from vaccinees receiving three doses of ZF2001, three doses of inactivated vaccines, or two inactivated doses plus ZF2001 booster showed high neutralizing titers against prototype and BA.2 but diminished efficacy against BA.4, BA.4.6, BF.7, BQ.1, BQ.1.1, and XBB—especially those with R346T mutations. Seropositivity dropped sharply for BQ.1, BQ.1.1, and XBB. Murine serum testing with next-generation heterodimeric RBD constructs (e.g., Delta–BA.2) revealed broader immune responses, especially from Delta–BA.2 RBD-dimer, which generated high neutralizing titers even against immune-evasive subvariants. Authors advocate updated vaccine designs to overcome resistance and highlight ongoing evaluation of ZF2202 in clinical trials.

   This correspondence reports on the neutralization capacity of ZF2001 (homotypic RBD-dimer vaccine), inactivated-virus vaccines, and chimeric RBD-dimer immunogens against emerging SARS-CoV-2 Omicron subvariants. Human serum from vaccinees receiving three doses of ZF2001, three doses of inactivated vaccines, or two inactivated doses plus ZF2001 booster showed high neutralizing titers against prototype and BA.2 but diminished efficacy against BA.4, BA.4.6, BF.7, BQ.1, BQ.1.1, and XBB—especially those with R346T mutations. Seropositivity dropped sharply for BQ.1, BQ.1.1, and XBB. Murine serum testing with next-generation heterodimeric RBD constructs (e.g., Delta–BA.2) revealed broader immune responses, especially from Delta–BA.2 RBD-dimer, which generated high neutralizing titers even against immune-evasive subvariants. Authors advocate updated vaccine designs to overcome resistance and highlight ongoing evaluation of ZF2202 in clinical trials.