Background Antibody response after vaccination is a surrogate measure of vaccine efficacy. Studies exploring the association between post-vaccination antibody levels and protection against infections after immunization with pneumococcal conjugate vaccine in adult patients with arthritis are lacking.
Objectives To investigate the association between antibody response after vaccination and occurrence of putative pneumococcal infections up to 53 months after vaccination with 7-valent pneumococcal conjugate vaccine (PCV7) in patients with rheumatoid arthritis (RA) and spondylarthropathy (SpA).
Methods A cohort of 497 patients with rheumatoid arthritis (RA; n=248) and spondylarthropathy (SpA; n=249) including psoriatic arthritis, regularly followed at the outpatient rheumatology clinic, Skåne University Hospital in Lund and Malmö, was immunised with a single dose of PCV7. At vaccination, patients were treated with methotrexate (MTX) (n=84), anti-TNF+MTX (n=169) or anti-TNF as monotherapy (n=158) or NSAIDs/analgesics (only SpA patients; n=86). Antibody levels for 6B and 23B were measured before and 4-6 weeks after vaccination using ELISA. Positive antibody response was defined as ≥2-fold increase in pre-vaccination antibody levels. Vaccinated patients with a history of putative serious pneumococcal infections were identified in the Skåne Healthcare Register using ICD-10 diagnostic codes. Serious infections included: pneumonia, other lower respiratory infections, meningitis, sepsis and septic arthritis. All events occurring up to 4.5 years after vaccination were retrieved. Relation between post-vaccination antibody levels and severe infection was explored using relation receiver operating characteristic (ROC) curves for each serotype separately.
Results Results. Between May 2008 and December 31st 2012 in total 27 serious infections were identified in 23 patients (4.6%) (4 patients had 2 infections). Geometric mean titers (GMT) for 6B and 23F were calculated using logarithmic transformed pre- and post-vaccination antibody titers (Table). Patients with serious infections had significantly lower post-vaccination antibody titers for both serotype 6B (p=0.040) and 23F (0.036; Mann Whitney U-test). ROC curves identified cut-off levels of 1.17 mg/L (70% specificity and 39% sensitivity) for serotype 23F and 1.23 mg/L (76% specificity and 35% sensitivity) for serotype 6B.
Conclusions Patients with a history of a serious infection after vaccination had lower antibody levels compared to those without such infections. Cut-off levels of post-vaccination antibody titers associated with protection for serious infections corresponded to those of ≥1 mg/L being generally considered as protective at our laboratory. Frequency of positive antibody response to vaccination did not differ between patients with and without serious infections.
Disclosure of Interest None declared