Direct effectiveness of pneumococcal polysaccharide vaccine against invasive pneumococcal disease and non-bacteremic pneumococcal pneumonia in elderly population in the era of pneumococcal conjugate vaccine: A case-control study

Abstract

Background: While herd effects and serotype replacement by childhood pneumococcal protein conjugated vaccines (PCVs) continues to accumulate worldwide, direct effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) against pneumococcal diseases in the elderly has been challenged. We estimated the direct effectiveness of PPV23 in the elderly population.

Methods: For a hospital-based case-control study, cases of invasive pneumococcal disease (IPD) and non-bacteremic pneumococcal pneumonia (NBPP) (adults ≥ 65 years) were identified in 14 hospitals participated in the pneumococcal surveillance program from March 2013 to October 2015, following implementation of PPV23 national immunization program (NIP) for the elderly in the Republic of Korea. Controls matched by age, sex, and hospital were selected at ratios of 1:2 (IPD) or 1:1 (NBPP). Clinical data and vaccination records were collected. Vaccine effectiveness was calculated as (1-adjusted odds ratio) × 100.

Results: We enrolled 148 IPD and 557 NBPP cases, and 295 IPD and 557 NBPP controls for analyses. Overall effectiveness of PPV23 against IPD was 28.5% [95% confidence interval (CI) -5.8%-51.6%] and against NBPP was 10.2% (-15.1-30.6) in all patients ≥ 65 years. However, in subgroup analysis of patients aged 65-74 years, PPV23 was protective against IPD [effectiveness 57.4% (19.4-77.5)] and against NBPP [effectiveness 35.0% (2.3-56.7)]. Furthermore, serotype-specific effectiveness of PPV23 against IPD was 90.6% (27.6-98.8) for PPV23-unique serotypes and 81.3% (38.6-94.3) for PPV23 serotypes excluding serotype 3.

Conclusions: This study indicates that PPV23 with broad serotype coverage might be beneficial in preventing IPD and NBPP due to non-PCV13 serotypes in the young-elderly, with potentially increasing effectiveness in the setting of childhood PCV NIP.

Keywords: 23-valent pneumococcal vaccine; Case-control study; Effectiveness; Pneumococcal infections; Streptococcus pneumoniae.