Discussion
In the present study, we show that SOTRs have weak neutralizing antibody responses against the SARS-CoV-2 B.1 and Omicron BA.1 variants even after two boosters with the BNT162b2 mRNA vaccine. Importantly, those SOTRs not responding to the first vaccination scheme do not show an increase in their NAb titers upon one and two boosters (Recently, a meta-analysis showed that booster vaccination enhances the immunogenicity of COVID-19 vaccines in SOTRs, however, a significant share of the recipients still has not built a detectable humoral immune response after the 3rd dose (