Pneumococcal serotype-specific IgG and opsonophagocytic activity in young Japanese patients with asplenia

Patients with asplenia are at high risks of severe infections caused by encapsulated bacteria, particularly Streptococcus pneumoniae. Thirteen-valent pneumococcal conjugate vaccine (PCV13) and 23-valent pneumococcal polysaccharide vaccine (PPSV23) are recommended for invasive pneumococcal disease prevention; however, little is known about the immunity to pneumococci in young patients with asplenia. We measured pneumococcal serotype-specific IgG (Pn-IgG) levels and pneumococcal opsonophagocytic activity (Pn-OPA) against some PCV13-contained serotypes (1, 3, 5, 6A, 7 F, 19A) in 23 young patients with asplenia using surplus serum samples. In this study, 5 and 13 patients had received PCV13 during routine immunizations and PPSV23, respectively; however, >5 years had passed since the last dose in most cases. The geometric mean concentrations (GMCs) of Pn-IgG in all study patients were not under the cutoff level against six serotypes, but they were lower than the those of age-matched healthy controls, as we have previously published. The patients who had received only PPSV23 had significantly lower GMCs against four serotypes (serotypes 1, 6A, 7 F, and 19A) than that of the patients who had received at least one PCV13 vaccination. The patients who had received only PPSV23 also had significantly lower geometric mean titers (GMTs) of Pn-OPA against all three serotypes we measured (serotypes 3, 5, and 19A) than that of the patients who had received at least one PCV13 vaccination. Our findings are useful data that can indicate insufficient immunity in young patients with asplenia against some PCV13 pneumococci serotypes and suggest the need for appropriate vaccinations in the post-PCV13 era.