SARS-CoV-2 Antibody Response to 2 or 3 Doses of the BNT162b2 Vaccine in Patients Treated With Anticancer Agents.

Patients with solid cancer are more susceptible to develop SARS-CoV-2 infection and severe complications; the immunogenicity in patients treated with anticancer agents remains unknown. To assess the immune humoral response to 2 or 3 doses of the BNT162b2 (BioNTech; Pfizer) vaccine in patients treated with anticancer agents. A prospective observational cohort study was conducted between February 1 and May 31, 2021. Adults treated with anticancer agents who received 2 or 3 doses of vaccine were included; of these, individuals with a weak humoral response 1 month after the second dose received a third injection. Quantitative serologic testing of antibodies specific for SARS-CoV-2 was conducted before vaccination and during follow-up. Humoral response was evaluated with a threshold of anti-SARS-CoV-2 spike protein antibody levels at 1000 arbitrary units (AU)/mL to neutralize less-sensitive COVID-19 variants. Among 163 patients (median [range] age, 66 [27-89] years, 86 men [53%]) with solid tumors who received 2 or 3 doses of vaccine, 122 individuals (75%) were treated with chemotherapy, 15 with immunotherapy (9%), and 26 with targeted therapies (16%). The proportions of patients with an anti-S immunoglobulin G titer greater than 1000 AU/mL were 15% (22 of 145) at the time of the second vaccination and 65% (92 of 142) 28 days after the second vaccination. Humoral response decreased 3 months after the second dose. Treatment type was associated with humoral response; in particular, time between vaccine and chemotherapy did not interfere with the humoral response. Among 36 patients receiving a third dose of vaccine, a serologic response greater than 1000 AU/mL occurred in 27 individuals (75%). The results of this cohort study appear to support the use of a third vaccine dose among patients with active cancer treatment for solid tumors.