744. Effectiveness of 23-Valent Pneumococcal Polysaccharide Vaccine and Influenza Vaccine Against Pneumococcal Pneumonia Among Elderly Patients Aged 65 Years and Older in the Republic of Korea: A Case–Control Study

BACKGROUND: The national immunization program (NIP) of annual influenza vaccination to the elderly population (≥65 years of age) in the Republic of Korea (ROK) has been implemented since 1987. Recently, the 23-valent pneumococcal polysaccharide vaccine (PPV23) through the NIP has been provided to the elderly population in the ROK since May 2013. The aim of this study was to assess PPV23 and influenza vaccine (IV) effectiveness in preventing pneumococcal pneumonia (PP) among elderly patients ≥65 years of age. METHODS: A case–control study using a hospital-based cohort was conducted. Cases of PP including bacteremic PP and nonbacteremic PP were collected from 14 hospitals in the pneumococcal diseases surveillance program from March 2013 to October 2015. Controls matched by age and sex in the same hospital were selected. Demographic, clinical information, and vaccination histories were collected. Previous immunization was categorized into “vaccinated” if a patient had received vaccines as follows: PPV23 (4 weeks to 5 years) and IV (2 weeks to 6 months) prior to the diagnosis of PP for case patients and prior to the hospital admission for control patients. Adjusted odds ratio (OR) was calculated, controlling for underlying medical conditions. Vaccine effectiveness was defined as (1 – OR) × 100. RESULTS: During the study period, a total of 661 cases (104 bacteremic PP cases and 557 nonbacteremic PP cases) and 661 controls were enrolled for analyses. For overall patients ≥65 years of age, there was no significant vaccine effectiveness against PP. For young elderly patients with 65–74 years, IV alone (1.2%, [95% confidence interval (CI) −95.3% to 50.0%]) and PPV23 alone (21.9%, [95% CI −39.0% to 56.1%]) were not effective. However, significant vaccine effectiveness of PPV23 plus IV against PP was noted (54.4%, [95% CI 6.9–77.7%], P = 0.031). For older elderly patients ≥75 years of age, no significant vaccine effectiveness was observed. CONCLUSION: Our study indicates that PPV23 plus IV may be effective in preventing PP among young elderly patients with 65–74 years, suggesting additive benefits of influenza plus PPV23 vaccination. Further studies are required to confirm the persistent additive protective effectiveness. DISCLOSURES: All authors: No reported disclosures.