Humoral serologic response to the BNT162b2 vaccine after allogeneic haematopoietic cell transplantation.

Objectives Assess the humoral immune response to the BNT162b2 vaccine after allogeneic haematopoietic cell transplantation (HCT). Methods This is a prospective cohort study. The SARS-CoV-2 IgGII Quant (Abbott©) assay was performed 4 to 6 weeks after the second BNT162b2 vaccine for quantitative measurement anti-spike antibodies. Results The cohort included 106 adult patients. Median time from HCT to vaccination was 42 (range: 4 to 439) months. Overall, 15/106 (14%, 95% confidence interval (CI): 7% to 21%) were seronegative despite vaccination, 14/52 (27%, 95%CI: 19% to 35%) of patients on immunosuppression compared to only 1/54 (1.8%, 95%CI: 1% to 4%) of patients off immunosuppression (p=0.0002). The proportion of seronegative patients declined with time; it was 46% (6/13) during the first year, 12.5% (3/24) during the second year and 9% (6/69) beyond 2 years from transplant. Patients with acute graft-vs.-host disease (GVHD) (odds ratio (OR): 3.3, 95%CI: 0.97 to 11.1, P=0.06) and moderate to severe chronic GVHD (OR: 5.9, 95%CI: 1.2 to 29, P=0.03) were more likely to remain seronegative. Vaccination was well tolerated by most patients. Yet, 7% (7/106) reported that GVHD-related symptoms worsened within days following vaccination. Conclusion A significant proportion of allogeneic HCT recipients receiving immunosuppression demonstrated an inadequate humoral response to the BNT162b2 vaccine. These patients should be recognised and instructed to take appropriate precautions. Recipients who were off immunosuppression had a humoral response that was comparable to that of the general population.