Second-dose covid vaccine (BNT162b2) efficacy in allogeneic HSCT recipients

September 2021 Prevention Tobias Rawson

Patients who have recently received a haematopoietic stem cell transplant (HSCT) have a particularly dismal prognosis following covid-19 infection. The overall survival (OS) for these patients at 30 days post-diagnosis is 68% and 67% for allogeneic HSCT and autologous HSCT patients, respectively. Furthermore, these patients have been excluded in vaccine efficacy studies, and so the efficacy of covid vaccination is unknown in this patient population. Published recently in The Lancet, a study of 88 allogeneic HSCT recipients investigated the efficacy of a second dose of the BNT162b2 mRNA vaccine, produced by Pfizer-BioNTech.  

Spike glycoprotein-specific IgG receptor-binding domain (IgG[S-RBD]) levels were assayed for at a median of 28 days, post-2nd vaccination, at a median time of 23 months since these patents received a HSCT. An IgG (S-RBD) titre of 4160 AU/mL was used a threshold, as this had previously been reported as corresponding to a 0.95 probability of viral neutralisation.

Immunosuppression results in sub-protective titres

Comparing patient characteristics in relation to the threshold value, a time interval greater than or equal to 12 months between HSCT and vaccination was associated with a protective IgG titre (multivariate OR[95%CI]: 1.3[0.3-5.1], P= 0.69), as was having a total lymphocyte count ≥1 G/L (multivariate OR[95%CI]: 6.4[1.2-3.4], P= 0.03). In contrast, patients who had received systemic immunosuppression within 3 months before vaccination had sub-protective IgG titres (multivariate OR[95%CI]: 0.07[0.02-0.25], P< 0.001). Overall, 52 patients had titres above 4160 AU/mL, and 36 patients had titres below this threshold.

This first evaluation of immunogenicity of the BNT162b2 covid vaccine in HSCT recipients found frequent and protective levels of humoral response. Furthermore, lymphocyte count and pharmacological immunosuppression were found to be predictive of immunogenic response. These findings support the vaccination of these patients, although larger studies are still required to determine, with accuracy, the level of immunological response observed in these patients.     

Reference:

Redjoul R, Bouter AL, Beckerich F et al., Antibody response after second BNT162b2 dose in allogeneic HSCT recipients. Lancet. 2021; 398(10297): 298-299.

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