Objective: Cancer patients are among the high-risk groups where COVID-19 infection tends to be severe and can lead to increased mortality. Therefore, they are included in the priority groups for COVID-19 vaccination. This study aimed to compare the levels of SARS-CoV-2 immunoglobulin G (IgG) antibodies following two different COVID-19 vaccinations between hematology-oncology patients and healthcare personnel and to identify factors associated with these antibody levels.
Patients and methods: A prospective study was conducted with 91 hematology-oncology patients (cancer group) and 75 healthcare personnel (control group) from January 2020 to June 2023. The cancer and control groups comprised adults who had received a booster dose, with either a single dose of BNT162b2 or two doses of CoronaVac™ spaced one month apart, following their primary vaccination with two doses of either CoronaVac™ or BNT162b2. Four weeks after the administration of the booster dose, levels of SARS-CoV-2 IgG antibodies were assessed using an ELISA kit. Antibody levels above 50 AU/mL were accepted as signifying seropositivity.
Results: The median SARS-CoV-2 IgG antibody level was lower in the cancer group compared to the control group (4,509 vs. 7,268, p = 0.004), while the rate of seroconversion was similar between the groups (97.8% vs. 100%, p = 0.564). In the cancer group, no association was found between SARS-CoV-2 IgG antibody levels and age, sex, comorbidity, type of malignancy, stage and duration, or type of vaccine.
Conclusions: In cancer patients, the seroconversion positivity rate was about 98%. However, antibody responses were still lower compared to the control group. No difference was detected in antibody levels among cancer patients based on the type of vaccine.