Neutralizing antibody responses to the primary series of a COVID-19 mRNA vaccine in the cancer cohort under active treatment.

Individuals with cancer are at increased risk of severe COVID-19 and immunogenicity of SARS-CoV-2 vaccines may be compromised, especially in those receiving systemic anti-cancer treatment. Understanding how treatment affects vaccine-induced humoral responses is critical to optimize vaccination strategies in this vulnerable population. This study evaluated neutralizing antibody responses to SARS-CoV-2 vaccination in cancer cohorts undergoing active treatment or not, measured at multiple timepoints before and after vaccination using a pseudovirus-based neutralization assay. We observed significantly lower seroconversion rates and impaired neutralizing antibody responses in the cancer cohort on active treatment compared to those not on treatment, suggesting an association between active treatment and a compromised functional immune response. Although strong correlations between anti-spike IgG and neutralizing antibodies were observed across all groups, regression analyses revealed potential differences in the relationship between binding and functional antibodies. We also observed the correlation between avidity and neutralizing antibodies varied across groups. These findings suggest that active systemic therapy impaired both the quantity and quality of antibody responses. Tailored vaccination timing and monitoring may be critical in reducing the risk of severe COVID-19 symptoms and improving COVID-19 vaccine efficacy in this population.