Abstract

Purpose
Current guidelines recommend vaccination at least two weeks before chemotherapy initiation to optimize the immune response despite limited evidence. Our previous study indicated no differences in short-term immune response for the 13-valent pneumococcal conjugate vaccine (PCV13) according to the vaccination timing. This study aims to investigate the long-term efficacy of PCV13 and clinical factors associated with the respective antibody response.
Materials and Methods
Patients with gastric or colorectal cancer who received adjuvant chemotherapy were enrolled and divided into two groups: vaccinated two weeks before chemotherapy (arm A) and vaccinated concurrently with chemotherapy (arm B). Serum samples were collected before vaccination and in one month, three years, and five years. Immune responses were measured using ELISA and multiplex opsonophagocytosis assay.
Results
Including 63 patients, both groups showed an initial increase in the geometric mean titers (GMTs) of opsonophagocytic activity and the geometric mean concentrations (GMCs) of serotype-specific IgG levels after one month, followed by a decline at three and five years, particularly for serotypes 1, 14, 18C, and 19A. Despite the decline, global protection was maintained for five years, although global response decreased. The two arms did not show significant differences in immunogenicity nor in factors such as vaccination timing, age, cancer type, or chemotherapy regimen.
Conclusion
Vaccination timing is not a significant factor for the immunogenicity of PCV13 in cancer patients undergoing adjuvant chemotherapy. Global protection against pneumococcal infection was sustained for >5 years, and global response remained in over half of patients.

• Keywords: Pneumococcal vaccines, Chemotherapy, Adjuvant, Stomach neoplasms, Colorectal neoplasms