Influenza Vaccine Effectiveness Against Influenza-Associated Pneumonia and Pneumococcal Pneumonia in Older Adults: A Prospective Test-Negative Design Study

Abstract

BackgroundStudies have shown that influenza vaccines are effective in preventing influenza-associated acute respiratory illnesses in older adults. However, the influenza vaccine effectiveness (IVE) against influenza-associated pneumonia in this age group has not been established. No study has formally investigated the IVE against pneumococcal pneumonia.MethodsThis study was conducted as part of a multicenter prospective investigation of adult pneumonia by the Adult Pneumonia Study Group-Japan (APSG-J). All community-onset pneumonia patients aged 65 years or older who visited a community-based hospital in Chiba, central Japan were enrolled to the study from December 2012 to January 2014. Sputum samples were tested for 13 viruses and 6 bacteria by multiplex PCR assays. Patients were diagnosed as influenza-associated pneumonia if sputum PCR assays were positive for influenza A or B. Patients were diagnosed as pneumococcal pneumonia if sputum culture yielded pneumococcus, sputum PCR assays were positive for both ply and lytA genes, or a urinary antigen test showed a positive result. Patients were considered vaccinated if they had received at least one dose of seasonal inactivated influenza vaccine in the 12 months before the hospital visit. A test-negative design was applied to estimate the IVE for influenza-associated pneumonia and pneumococcal pneumonia. IVEs were calculated as (1 – odds ratio) × 100%.ResultsA total of 1044 patients were enrolled to the study. Among them, 49 (4.7%) were influenza-associated pneumonia, and 168 (16.1%) were pneumococcal pneumonia. The adjusted IVE against influenza-associated pneumonia was 57.2% (95% CI, 17.9% to 76.8%). The adjusted IVE against pneumococcal pneumonia was 31.7% (0.6% to 53.1%); the estimate did not change before and after controlling for pneumococcal vaccination history.ConclusionInfluenza vaccines effectively prevent influenza-associated pneumonia in older adults. Influenza vaccines are also associated with decreased risk of pneumococcal pneumonia in this age group, while some residual confounding may remain.Disclosures All authors: No reported disclosures.