Severe invasive pneumococcal disease beyond current vaccination recommendations: implications for higher-valency vaccines.

Objectives

To describe the epidemiology, clinical characteristics, and serotype distribution of invasive pneumococcal disease (IPD) in adults in Southern Switzerland, and to evaluate the theoretical coverage of higher-valency pneumococcal conjugate vaccines, with particular focus on patients without current vaccination indications.

Methods

This retrospective study included all adults with microbiologically confirmed IPD admitted to four hospitals in Southern Switzerland between January 2019 and December 2024. Clinical data, serotypes, and vaccination status were collected. Theoretical vaccine coverage was calculated for PCV13, PCV15, PCV20, and PCV21. Multivariable logistic regression identified predictors of intensive care unit (ICU) admission and mortality.

Results

Among 210 patients (mean age 69.3 years), 79 (37.6%) were admitted to the ICU and 18 (8.6%) died. Charlson Comorbidity Index was the only independent predictor of both ICU admission (OR 1.25, 95% CI 1.02-1.57) and mortality (OR 2.37, 95% CI 1.54-3.64). Serotype 8 was the most frequent isolate (21.0%), followed by serotypes 3 (13.3%) and 4 (9.5%). Only 9.9% of patients had received prior pneumococcal vaccination. Fifty-six patients (26.7%) were aged < 65 years without comorbidities and had no vaccination indication; 44.6% of these were admitted to the ICU. Serotype 8 accounted for 30.4% of infections in this subgroup. PCV13 and PCV15 would have covered 28.6% and 33.9% of cases in non-eligible adults, whereas PCV20 and PCV21 would have covered 67.9% and 73.2%, respectively.

Conclusions

More than one-quarter of adult IPD occurred in individuals without current vaccination indications, with high rates of severe disease. Higher-valency conjugate vaccines could substantially expand serotype coverage in this population, supporting reconsideration of age-based vaccination strategies.