The Humoral Response of Patients With Cancer to Breakthrough COVID-19 Infection or the Fourth BNT162b2 Vaccine Dose.

Since January 2022 in Israel, high-risk populations with underlying health conditions were advised to receive a fourth dose of the BNT162b2 vaccine (Pfizer-BioNTech) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We monitored vaccine-induced immunity among oncology patients undergoing systemic anti-cancer therapy before and after the 4th-BNT162b2-dose. Three groups of patients were included in the study: those who received 3rd-BNT162b2-dose and had no breakthrough infection (control), those who received 3rd-BNT162b2-dose and had the breakthrough infection, and those who received the 4th-BNT162b2-dose and had no breakthrough infection.