Chronic disease and immunosuppression increase the risk for non-vaccine serotype pneumococcal disease - a nationwide population-based study.

BACKGROUND: Demography is changing, with people living longer with comorbidities. In this nationwide population-based study, we investigated the serotype-specific invasive pneumococcal disease (IPD) risk in individuals with comorbidities, and effects of the pneumococcal conjugated vaccine (PCV) child immunization program.

METHODS: Cases included 14096 serotyped IPD episodes in Sweden between 2006-2015. Controls (n=137289), matched to cases by age, sex, region, and calendar time, were selected from the general population. Comorbidity data was obtained through health registers and grouped as immunocompromising (IC) or chronic medical conditions (CMC).

RESULTS: The prevalence of CMC and IC among elderly IPD cases was 33.9% and 39.4%. New risks identified for IPD were Sarcoidosis, Inflammatory polyarthropathies, Systemic connective tissue, and neurological diseases. The odds ratio (OR) for IPD caused by non-PCV13 compared to PCV13 serotypes, was higher in individuals with CMC/IC. Serotypes associated with the highest risk were non-PCV13 serotypes 16F, 15C, 35F, 19F and 23A (OR 3-5 for CMC, >10 for IC). Most comorbidities increased post-vaccination and absolute increases of IPD caused by non-PCV13, PPV23-non-PCV13, and non-PCV13/non-PPV23 serotypes, were higher in individuals with IC/CMC compared to healthy persons. Non-PCV13 serotypes 6C, 9N, 11A, 22F, 23A and 35F increased more in those with comorbidities. The mortality due to non-PCV13 serotypes increased in individuals with IC/CMC, while remaining stable in persons without comorbidities.

CONCLUSION: The PCV child immunization program is associated with an increased disease burden of non-vaccine serotypes in individuals with comorbidities. These data are important for vaccine design and optimization of current vaccination strategies.