Factors affecting the serologic response to SARS-CoV-2 vaccination in patients with solid tumors: A prospective study

To evaluate the factors affecting seropositivity and antibody levels after SARS-CoV-2 vaccines in patients with cancer because they were excluded from clinical studies of SARS-CoV-2 vaccines.

This prospective, observational, single-center study included 290 patients with solid tumors followed up in our medical oncology clinic between March 2021 and August 2021. SARS-CoV-2 antibody status was determined before the first dose of vaccine. Fifty-one patients with positive prevaccine baseline antibody tests were excluded from the study, regardless of whether they had previously confirmed SARS-CoV-2 PCR positivity. To determine the quantitative IgG antibody response of the vaccines, blood samples were collected at least 28 days after each dose of vaccine. Quantitative IgG levels against virus spike protein receptor binding domain (RBD) were measured using chemiluminescent enzyme immunoassay (CLIA). Demographic and clinical features affecting seropositivity were analyzed.

One hundred and fifty-one (69.3%) patients were vaccinated with two doses of CoronaVac followed by one dose of BNT162b2 (Biontech) (group 1). Sixty-seven (30.7%) patients were vaccinated with three doses of BNT162b2 (group 2). The proportion of patients who developed seropositivity was significantly higher in group 2 (78.6% vs. 54.9%, p < 0.012). Antibody response increased significantly after the second dose of vaccine in both groups. Female sex, being younger than 65 years, and chemotherapy status were significantly related to higher anti-SARS-CoV-2 S antibody levels (p = 0.033, p = 0.036, and p = 0.047, respectively). Antibody levels were significantly higher in patients who had previously received chemotherapy than in patients receiving active chemotherapy (p = 0.042).

Our study is the first to evaluate basal SARS-CoV-2 IgG levels before the first dose of vaccine and after three doses in patients with solid tumors. The rate of development of seropositivity with two doses of mRNA vaccine was found to be higher than with two doses of inactivated SARS-CoV-2 vaccine. More attention should be paid to preventive measures in addition to vaccination in patients aged over 65 years and men with cancer diagnoses.