Antibody Response after BNT162B2 COVID-19 mRNA Vaccination in Cancer Patients Under Anti-Neoplastic Treatment

Background: Cancer patients are at higher risk of developing severe COVID-19. However, safety and efficacy of COVID-19 vaccination in cancer patients undergoing treatment is unclear. Methods: In this interventional prospective multi-cohort study, priming and booster doses of the BNT162b2 COVID-19 vaccine were administered 21 days apart to solid tumor patients receiving chemotherapy, immunotherapy, targeted- or hormonal therapy, and patients with a hematologic malignancy receiving rituximab or after allogeneic hematopoietic stem cell transplantation. Primary endpoint was anti-SARS-CoV-2 receptor binding domain (RBD) antibody level at 28 days post-booster. Anti-RBD IgG titers above 200 IU/ml was used to define high-responders as it leads to a neutralization response required for 50% protection against symptomatic SARS-CoV-2 infection in 268 independent subjects. Secondary endpoints included self-reported adverse events (AEs), antibody response over time and number of breakthrough infections after vaccination. Findings: 28 days post-booster vaccination of 197 cancer patients, antibody response was lower in the hematological cohort (geometric mean titer (GMT) 17·61 IU/mL [95% CI 7·17-43·24]) and the chemotherapy cohort (GMT 234·05 IU/mL [95% 95%CI 122·10-448·66]) when compared to healthy individuals (n=40; GMT 1844·93 IU/mL [95% CI 1383·57-2460·14]), irrespective of timing of vaccination during chemotherapy cycles. Only 55% and 7% of patients receiving chemotherapy or rituximab could be categorized as high-responders at 28 days post-booster. During the study period, five subjects tested positive for SARS-CoV-2 infection, including three after full vaccination. Local and systemic AEs were mostly mild to moderate, with only 1-3% of patients experiencing severe AEs. Local, but not systemic, AEs occurred more frequently after booster than after priming dose. Interpretation: The BNT162b2 vaccine is well-tolerated in cancer patients under active treatment. However, the antibody response of immunized cancer patients was delayed and diminished, mainly in patients receiving chemotherapy or rituximab, resulting in breakthrough infections. Trial Registration: EudraCT number 2021-000300-38 Funding: The regulatory sponsor was the Antwerp University Hospital (EudraCT number 2021-000300-38). The trial was funded by the Belgian Government through Sciensano (COVID-19_SC004, COVID- 19_SC059, COVID-19_SC061). Declaration of Interest: MP declares to have an advisory role within Remedus, all other authors declare no competing interests. Ethical Approval: The study was approved by the local ethics committee and was executed in accordance with Good Clinical Practice and the Declaration of Helsinki (ICH GCP E6(R2)).