COVID-19 vaccinations are predicted to be a huge success in pandemic control. However, the majority of the studies were conducted on healthy individuals, and the efficiency of COVID-19 vaccination in post-transplant patients is uncertain. In the setting of HSCT, the extreme immunosuppression caused by the conditioning regimen and the graft versus host disease (GvHD) preventive regimen clearly has an impact on the efficacy and immunogenicity of the COVID-19 vaccine. Given the importance of eliciting early SARS-Cov-2 protective immunity in patients who are undergoing Allo-HSCT and the EBMT recommendation to endorse vaccination as early as 3 months after allo-HCT [7], we conduct this prospective study to investigate the safety and immunogenicity of three doses Pastucovac (an RBD-based SARS-Cov-2 vaccine) at the early post-transplant period in adult Iranian patients who are undergoing Allo-HSCT. We also want to see whether there are any possible predictors, such as the effect of clinical characteristics and lymphocyte subpopulations at the time of vaccination on the serologic response following immunization. The findings of this study will serve to guide future COVID-19 vaccination recommendations in this population, such as the optimal starting time, interval time, and so on.

From the start of the study until the sample size of 100 patients is attained, all consecutive adult patients who are candidates for Allo-SCT at HORCSCT, sign a research project consent to administer SARS-CoV-2 vaccination with Pastucovac, and sign a permission to take pre-and post-vaccination blood samples for deposit to the research database, are enrolled in the study. At baseline (before conditioning) and day +30 post-transplant, peripheral blood samples are taken to test particular lymphocyte subpopulations and SARS-CoV-2 IgG titers.

All enrolled post-Allo-SCT participants who meet the inclusion criteria including; age ≥ 18 years, successfully engraftment with full donor chimerism, absence of grade 3,4 acute GvHD or severe extensive chronic GvHD, no receive more than 0.5 mg/kg prednisolone, and no positive RT-PCR test for COVID-19 following HSCT are recruited to study from 3 to 12 months after Allo-HSCT and vaccinated with 2 doses of Pastucovac, with a 4-week (±7 days) interval and a booster dose with an 8-week (±7 days) interval from the second dose. Peripheral blood samples are collected before the first dose of vaccine to assess certain immune reconstitution and SARS-CoV-2 IgG titer. The serologic response against the SARS-CoV-2 spike protein (anti-S) is assessed in serum four weeks (± one week) after the first vaccine dose (before the second vaccine), four weeks (± one week) after the second dose, and four weeks (± one week) after the booster dose (third dose).

Inclusion Criteria:

Age ≥ 18 years, successfully engraftment with full donor chimerism, absence of grade 3,4 acute GvHD or severe extensive chronic GvHD, no receive more than 0.5 mg/kg prednisolone, and no positive RT-PCR test for COVID-19 following HSCT

Exclusion Criteria:

Patients who are not candidates for the COVID-19 vaccine after transplantation due to severe complications.

Patients who do not consent to vaccination after transplantation