S typhi Vi Capsular Polysaccharide Vaccine-Induced Humoral Immunity in Travelers with Immunosuppressive Therapy for Rheumatoid Disease.

INTRODUCTION:
Typhoid fever is a global health problem, causing significant morbidity and mortality. Currently, the most widely used vaccine is the typhoid Vi capsular polysaccharide (Vi-PS) vaccine. While epidemiological studies on its efficacy have been performed in children in endemic countries, there are no efficacy studies evaluating its use in travel medicine. Response to vaccination may differ in travelers receiving immunosuppressive therapy. This study investigates the humoral response to Vi-PS vaccination in travelers receiving immunosuppressive therapy for rheumatoid disease.
METHODS:
We recruited patients from the LUMC rheumatology outpatient clinic and travelers from the travel clinic who had previously received Vi-PS vaccination and received immunosuppressive therapy for rheumatoid disease. We analyzed blood samples acquired from 42 patients over a period of 3 years. We estimated the length of persistence of protective titers using survival analysis using multiple cutoff values for protection, and measured titer half-life and the influence of immunosuppressive medication on titer half-life using mixed models.
RESULTS:
Anti Vi-PS antibody levels stayed above 10 EU/ml for a mean of 13.3 years, above 15 EU/ml for a mean of 10.1 years, and above 20 EU/ml for a mean of 8.6 years after Vi-PS vaccination. Titer half-life was 7.5 years (95% CI 5.0-14.7 years, P < 0.001). No significant influence of medication on titer half-life was found.
CONCLUSION:
Both persistence of protective antibody titers and titer half-life are longer than expected based on other studies. This warrants further study in adult volunteers, both in healthy individuals and patients suffering from rheumatoid disease.