Streptococcus pnemoniae is a major cause of morbidity and mortality among splenectomised patients with β-thalassemia major. We have previously shown that a 13-valent pneumococcal conjugate vaccine (PCV13) induces robust early immune responses in such patients, while history of repeated immunisations with the 23-valent polysaccharide pneumococcal vaccine (PPSV23) results in attenuation of the response to PCV13. However, the duration of vaccine-induced protection in splenectomised thalassemic patients and the associated need for booster immunisation remains unclear. In the current study, we enumerate antibody persistence 5 years post-PCV13 and investigate any correlation with early immune response and immunisation history. Pneumococcal serotype (PS)-specific antibodies against 5 vaccine antigens were measured 5 years post-PCV13 in 34 asplenic adults with β-thalassemia. PS-specific antibodies against 5 vaccine serotypes had declined significantly at 5 years post-PCV13 (year 5).Year 5 antibody titres remained above baseline for PS9V, 19A and19F, returned to baseline for PS23F, and dropped below baseline for PS3 (p < 0.001).Year 5 antibodies were positively correlated with day 28 antibody titres, while no correlation was found with early memory B cell response. Previous PPSV23 history was correlated with impaired antibody persistence against serotype 19A. Antibody levels dropped significantly but remained at protective levels 5 years post-PCV13.We propose that asplenic patients with β-thalassemia may benefit from measurement of antipneumococcal antibodies after 5 years post-PCV13 as they may eventually be in need for booster pneumococcal vaccination. Clinical Trials Registration ID: www.clinicaltrials.gov NCT01846923.
Keywords: Antibody persistence; Immunological memory; Pneumococcal vaccine; β-thalassemia major.