Discussion
The present study is the first trial comparing the homologous than heterologous prime-boost COVID-19 vaccination regimens throughout auto-HSCT recipients. In auto-HSCT patients who received two primary SARS-CoV-2 vaccines using RBD-TT conjugated platform, it was demonstrated that heterologous boosting with an inactivated platform yielded a superior serologic response and non-significantly more reactogenicity than homologous RBD-TT conjugated boosting. Exposure to various vaccine antigens could be attributed to the increased immunogenicity and reactogenicity identified following heterologous prim-boost COVID-19 immunization.In numerous investigations on the general population in Brazil, Korea, and Chile, consistent results on improved immune response following the heterologous than homologous booster immunization among participants who received two primary doses of the COVID-19 vaccine have been shown (Several studies have compared the immunogenicity of heterologous versus homologous booster vaccinations in solid organ transplants and immunocompromised patients (Study findings demonstrated that both homologous and heterologous booster vaccinations exhibited reasonable reactogenicity AEs during the first week following administration, either mild or moderate. Although there were more reactogenicity AEs with heterologous than homologous boosters, the two arms had no significant difference. Numerous studies undertaken in the general population have revealed greater reactogenicity with heterologous than homologous prime-boost vaccinations, supporting the study findings (Considering the predictors of immune response to booster doses, as shown in The study’s limitations, advantages, and other relevant considerations are as follows. The present study could not determine the exact amount of anti-S antibodies using a semiquantitative serologic test. Since it was impossible to access a functional assay kit for SARS-CoV-2-specific T-cell responses, cellular immunity could not be evaluated. Regarding benefits, all patients received two primary doses of RBD-TT conjugated SARS-CoV-2 vaccine (In conclusion, this blinded, randomly assigned controlled clinical trial shows that both homologous and heterologous prime-boost COVID-19 vaccination strategies are immunogenic and safe in auto-HSCT recipients primed with RBD-TT conjugated early after HSCT. However, heterologous prime-boost COVID-19 vaccination with inactivated platform resulted in considerably enhanced immune response and insignificantly higher reactogenicity than homologous RBD-TT conjugated prime-boost.