ABSTRACT
Background: Hematopoietic stem cell transplant recipients (HSCTs) may experience the diminished immunogenicity to COVID- 19 vaccines. Aim: To summarize current evidence on COVID-19 vaccine responses and risk factors for their attenuation in HSCTs. Methods: A literature was systematically searched and reviewed from the existence of databases through June 22, 2022. Descriptive statistics and random-effects model were used for a meta-analysis. Results: From 46 studies, representing 4446 HSCTs, the weighted mean (95% confidence interval [CI]) of positive antispike seroconversion after COVID-19 vaccines was 40% (30%-51%), 80% (77%- 83%), and 80% (69%-88%) for 1, 2, and 3 doses, respectively. The cellular immune response was 58% (40%-75%) after 2 doses. Notably, the risk factors (pooled odds ratio [95% CI]) for poor antibody response after 2 vaccine doses comprised recent rituximab exposure (0.10 [0.02-0.57]), haploidentical allografts (0.49 [0.28-0.87]), post-HSCT duration less than 24 months (0.22 [0.07-0.71]), lymphopenia (0.27 [0.16-0.45]), hypogammaglobulinemia (0.32 [0.22-0.47]), concomitant chemotherapy (0.48 [0.29-0.78]), immunosuppressants (0.22 [0.14-0.34]) and corticosteroids (0.29 [0.16-0.53]). Ongoing immunosuppressants (0.06 [0.00-0.81]) also increased risk of poor cellular immunogenicity. Conclusion: In HSCTs, humoral and cellular immunogenicity to 2-3 doses of COVID-19 vaccines are attenuated by several risk factors. Further efforts on COVID-19 prevention including neutralizing monoclonal antibody uses are needed for this vulnerable population.