Abstract 1612P
Background
A third dose booster vaccination is currently recommended in patients with cancer who were previously vaccinated with two doses of inactive COVID-19 vaccine based on the lower efficacy of the vaccines in these patients and waning of immunity over time. However, the data is limited on the efficacy of this vaccination strategy. We aimed to evaluate the seroconversion rates after two doses of inactive COVID-19 vaccine (CoronaVac) and the benefit of a third dose mRNA vaccine booster in patients with cancer receiving active treatment.
Methods
Patients with solid tumors receiving active treatment (n=101) and patients with no cancer (n=48) as the control group were included in the study. All the patients and controls had received two doses of CoronaVac and a third booster dose of the mRNA vaccine (Bnt162b2). Anti-SARS-CoV-2 Spike Receptor Binding Domain IgG antibody levels after the 2nd and 3rd dose were measured with quantitative ELISA.
Results
The median age of the patients was 66 (IQR 60-71). 79% of the patients were receiving chemotherapy, and 21% were receiving immunotherapy at the time of vaccination. Antibody levels measured after 2 doses of CoronaVac were significantly lower in patients with cancer than in the control group [median 0 μg/ml (IQR 0-1.17 μg/ml) vs. median 0.91 μg/ml (IQR 0-2.24 μg/ml), respectively, p=0.002]. Seropositivity rates were 46.5% in patients with cancer and 72.9% in the control group (p=0.002). Antibody measurement was performed in 26 patients after the third dose. Seroconversion rate increased from 46.5% to 88.5% (p<0.001), and the antibody titers significantly increased with the third-dose booster (median 0 μg/ml (IQR 0-1.17 μg/ml) after two doses vs. 12.6 μg/ml (IQR 1.8-69.1 μg/ml) after third booster dose, p<0.001).
Conclusions
In conclusion, our study provides important data regarding the lower efficacy of CoronaVac in patients with cancer compared with controls. Additionally, we demonstrated significantly increased seroconversion rates with a third-dose booster mRNA vaccine after two doses of CoronaVac in patients with cancer for the first time in literature. Further research is needed to define the optimal vaccination schedule in patients with cancer.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
This study was funded by Hacettepe University Scientific Research Projects Coordination Unit. Project number: THD-2021-19639.
Disclosure
All authors have declared no conflicts of interest.