295. Is Herd Immunity from Pneumococcal Conjugate Vaccines Changing the Clinical Features of Invasive Pneumococcal Disease in Adults

Abstract Background Numerous factors that affect the presentation and severity of pneumococcal disease. Several studies in the pre-PCV era demonstrated that organism characteristics, including serotype, are associated with variability in disease presentation and severity. We undertook an analysis of population based surveillance for invasive pneumococcal disease (IPD) to assess whether herd immunity from PCVs will change the presentation and severity of IPD in adults Methods TIBDN has performed population-based surveillance for IPD in Toronto and Peel region (pop’n 4.5M) since 1995. All sterile site isolates of S. pneumoniae are reported to a central study laboratory, isolates are serotyped, and clinical and vaccination data are collected via patient and physician interview and chart review. Population data are obtained from Statistics Canada. Backwards stepwise logistic regression assessed patient characteristics, illness features, and isolate factors associated with clinical presentation and case fatality. Results Between 1995 and 2018, 8815 episodes of IPD were identified in adults. Patients infected with PCV10not7 serotypes were younger, more likely male and without underlying illness. Patients with infections due to non-vaccine types were more likely to be immunocompromised. Case fatality in IPD declined from 177/754 in 1995/6 to 113/554 in 2017/8; OR 0.67, 95%CI0.51-0.86, P< .0001) and in all serotype groups (Figure). In multivariable models adjusted for host factors, relative to infections caused PCV7 serotypes, those caused by PCV10not7 were less likely to be fatal (OR 0.65, 95%CI 0.46–0.91); those caused by PCV13not10 were more likely to be fatal (OR 1.6, 95%CI 1.3–1.9). Bacteremic pneumonia as a proportion of presentations is highest in IPD due to PCV10not7 and PCV13not10 serotypes (85% and 83%, respectively), and lowest in IPD due to non-vaccine serotypes and PCV20not15 (59% and 68%, P< .0001). Meningitis is least common in IPD due to PCV10not7 serotypes (2.6%), and highest in cases due to non-vaccine types and PCV20not15 (9.0% and 8.0%, respectively, P< .0001). FIgure Conclusion In our population, herd immunity from PCVs will result in a higher proportion of adult IPD occurring in immunocompromised cases, and a shift from bacteremic pneumonia to bacteremia without focus and meningitis. Disclosures Allison McGeer, MD, FRCPC, GlaxoSmithKline (Advisor or Review Panel member, Research Grant or Support)Merck (Advisor or Review Panel member, Research Grant or Support)Pfizer (Research Grant or Support)