463. Immunogenicity and Safety of mRNA-based SARS-CoV-2 vaccination in Hematopoietic Stem Cell Transplant Recipients: A Systematic Review

BACKGROUND: Immunization is an effective strategy to decrease hospitalization and mortality related to SARS-CoV-2. Since the introduction of mRNA-based SARS-CoV-2 vaccines (BNT1261b2 and mRNA-1273), several studies have outlined the immunogenicity and safety of these in hematopoietic stem cell transplant (HSCT) recipients. Herein, we describe the first systematic review and meta-analysis with pooled data of available evidence on SARS-CoV-2 vaccination in this patient population. METHODS: We conducted a systematic review and meta-analysis of prospective cohort studies up to May 24 2022 in adult HSCT recipients who were vaccinated with ≥1 doses of either mRNA-based SARS-CoV-2 vaccine. The outcomes measured included: a) vaccine immunogenicity, b) safety, and c) breakthrough SARS-CoV-2 infections. Patients with solid organ transplant or prior documented history of SARS-CoV-2 infection were excluded. RESULTS: 1084 unique studies were identified. After abstracts review, 81 full-text studies were assessed by two independent reviewers. Twenty-nine studies were included. A total of 1738 patients were analyzed, out of which 1478 received allogeneic-HCST (Allo-HSCT) and 260 autologous-HSCT (Auto-HSCT). Median IgG positivity after at least 1 dose of vaccination (among studies) was 77.3% (range: 0-100%) among Allo-HSCT and 91.7% (range: 60-100%) among Auto-HSCT. Cellular immunity was reported in 5 studies, describing IFN-gamma and/or lymphocyte response. Median positivity was 42% (range: 24-78%) among Allo-HSCT. Pooled incidence of adverse events reported among all HSCT recipients was 38.72%. The most common side effect was injection-site pain. No grade 5 adverse events were described. De-novo or exacerbation of graft versus host disease was reported in the median of 2.28% (range: 0-6.6%) of Allo-HSCT recipients. Breakthrough COVID-19 infections were reported in both Allo-HSCT and Auto-HSCT in 1/479 (0.2%) and 2/254 (1.29%), respectively. [Figure: see text] CONCLUSION: mRNA-based SARS-CoV-2 vaccination was immunogenic in HSCT recipients, particularly among Auto-HSCT recipients. One or more doses of mRNA-based vaccine elicited a greater humoral response, compared to that of cellular immunity. Adverse events were common, but often were mild. Breakthrough infections are rare after ≥ 1 doses. DISCLOSURES: John M. Reynolds, MLIS, Pfizer Inc: Stocks/Bonds