Background: Recently published studies have found an impaired immune response after SARS-CoV-2 vaccination in solid organ recipients. However, most of these studies have not assessed immune cellular responses in solid organ transplant recipients. And no studies have yet demonstrated the efficacy of a booster (third) dose of SARS-CoV-2 vaccination in these patients. In this study, a prospective double-arm cohort study was performed to evaluate the humoral and the cellular immune response to SARS-CoV-2 vaccination in solid organ transplant recipients compared to healthy staff members with the normal function of the immune system.

Methods: A total of 64 transplant patients and an age-matched control group of 103 healthy staff members were included. Blood samples were obtained and analyzed after the second dose and the boosting (third) dose, respectively. For evaluation of the virus-neutralization capacity of each group, serum was analyzed using a surrogate SARS-CoV-2 neutralization test to quantify the functional inhibitory capacity of neutralizing antibodies (Genscript) against SARS-CoV-2 spike protein. Inhibition scores of under 30% was considered negative.

Results: Except the vaccination subgroup of the initial two dosages of AstraZeneca followed by Pfizer was significantly higher in the healthy control group, another prime-booster combination subgroup proportions were similar between the group. After the standard two doses of vaccination, only 28.3% of the transplant recipients demonstrated positive functional inhibition of neutralizing antibodies, significantly lower than 70.9% of the healthy control group (p <0.001). Even after the booster (third) dose of vaccination, 43.2% of the transplant recipients showed positive functional inhibition of neutralizing antibodies, significantly lower than 100% of the healthy control group (p <0.001). No other immune-associated complications such as acute rejection has occurred after SARS-CoV-2 vaccination in the transplant recipient group.

Conclusion: Our data strongly suggest revised vaccination approaches in immunocompromised patients, including individual immune monitoring for the protection of this vulnerable group at risk of developing severe COVID-19. It urges for a review of future vaccine strategies in these patients.