Chronic Disease and Immunosuppression Increase the Risk for Nonvaccine Serotype Pneumococcal Disease: A Nationwide Population-based Study

This nationwide study shows that pneumococcal nonvaccine-serotypes preferentially infect individuals with comorbidities. Pneumococcal conjugated vaccine introduction has shifted invasive pneumococcal disease caused by vaccine- to nonvaccine-serotypes in this patient group. The results are important for pneumococcal vaccination strategies. 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 14 096 IPD episodes in Sweden during 2006-2015. Controls (n = 137 289), 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 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 with PCV13 serotypes was higher in individuals with CMC/IC. Serotypes associated with the highest risk were 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 with healthy persons. Non-PCV13 serotypes 6C, 9N, 11A, 22F, 23A and 35F increased more in those with comorbidities. Mortality due to non-PCV13 serotypes increased in individuals with IC/CMC, while remaining stable in persons without comorbidities. Conclusions The PCV child immunization program associates 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.

Automated summary

This nationwide study demonstrates that individuals with comorbidities are more susceptible to infection by nonvaccine-serotypes of pneumococcus. The introduction of pneumococcal conjugated vaccine has led to a shift in the serotypes causing invasive pneumococcal disease in this patient group. These findings have significant implications for pneumococcal vaccination strategies.