Immune persistence of a single dose of 23-valent pneumococcal polysaccharide vaccine: A 6-year follow-up.

In a previous phase 3 clinical trial, a 23-valent pneumococcal polysaccharide vaccine (PPV23) induced robust immune responses in participants aged 2 years and older. We conducted this study to evaluate the immune persistence of a single dose of PPV23 6 years after vaccination. In this follow-up study, 600 participants aged 2 years and older (referred to the age of vaccination) who had received a single dose of either test vaccine or control vaccine in the previous clinical trial were enrolled in a 3:1 ratio. Blood samples were collected to determine anti-capsular immunoglobulin G (IgG) antibody levels against 23 serotypes with enzyme-linked immunosorbent assay (ELISA). A total of 598 subjects were included for immune persistence analysis. Six years after vaccination, the geometric mean concentrations (GMCs) of IgG antibodies to most serotypes remained higher than prior to vaccination in both groups (1.1-1.8 folds vs.1.1-1.7 folds), although there was a significant decrease compared to 28 days. The results suggested PPV23 could provide protection 6 years after vaccination. Considering the significant decrease of antibody level, the revaccination in high-risk population may be needed. ClinicalTrial.gov identifier: NCT03480763.