We also compared responses to the vaccine strain and Omicron variant spike protein S1 subunits and found that the breakthrough VRs made similar responses to the vaccine strain but more potent responses to the Omicron S1 protein than the postboost VRs (Figure 3B), indicating that T cell responses to Omicron variant are likely enhanced by breakthrough infections to this variant. Here, PSMD1 is linked to infection.