Protective effect of pneumococcal vaccination on pneumococcal pneumonia outcomes: analysis adjusted for severity and comorbidity.

BACKGROUND AND

OBJECTIVE

Pneumococcal vaccination may attenuate the severity of pneumococcal pneumonia even in breakthrough infections. However, evidence on this effect stratified by clinical severity is scarce. The objective was to evaluate whether vaccination reduces poor outcomes in patients hospitalized for pneumococcal pneumonia, specifically according to CURB-65 severity.

METHODS

Retrospective observational study of 90 adults with microbiologically confirmed pneumococcal pneumonia (January 2020-December 2024). Poor outcome was defined as death or ICU admission. Propensity score matching (PSM) 1:1 was performed to control for indication bias, adjusting for age, sex, comorbidity, CURB-65, and dependency. In the matched sample (43 pairs), the effect of vaccination on poor outcome was analysed with logistic regression further adjusted for comorbidity and CURB-65. Sensitivity analysis was conducted with inverse probability of treatment weighting (IPTW).

RESULTS

Vaccinated patients had higher age, comorbidity, and CURB-65 at admission. PSM achieved adequate balance between groups. In the matched sample, poor outcome occurred in 34.9% of vaccinated and 51.2% of unvaccinated (absolute reduction 16.3%). Adjusted OR for vaccination was 0.42 (95% CI: 0.16-1.07; p = 0.070), suggesting a possible protective effect, although statistical significance was not reached. CURB-65 was an independent predictor of poor outcome (OR per point: 1.93; p = 0.006). IPTW yielded an OR of 1.28 (95% CI: 0.67-2.47; p = 0.46).

CONCLUSIONS

Pneumococcal vaccination shows a possible protective effect, with a trend toward clinically relevant benefit, especially in patients with more severe disease (CURB-65 ≥ 3), reducing poor outcomes by 16.3%. This finding supports vaccination in adults with risk factors.