1517. Outcomes of Influenza Infection among Vaccinated and Un-Vaccinated Patients presenting to a Suburban hospital in Perth, Western Australia (WA), 2019 Southern Hemisphere Influenza Season

Abstract

Background Influenza season started in April, earlier than any previous season. WA immunization registry showed a higher than average vaccine uptake. By October 22,770 cases and 80 influenza related deaths were recorded (in 2018: 3,679 cases and 13 deaths). We aimed to characterize clinical presentation and outcomes of laboratory confirmed Influenza, comparing vaccinated with unvaccinated controls.Hypothesis; vaccination would result in less severe disease and better outcomes. Primary objective: length of stay (LOS); Secondary objective: prevalence of severe respiratory illness, ICU admission and death. Methods Retrospective study, April to October 2019. Eligible patients had a telephone-based questionnaire for clinical and immunization data verification. Excluded; < 18 years; deceased; dementia; nursing home and unable to consent. Continuous and categorical data of cases (vaccinated) and controls (unvaccinated) were compared using Mann-Whitney U test (non parametric), student t-test (parametric). Correlation and multilinear regression analyses were undertaken to determine the effects of vaccination status and identified confounders on the primary outcome. Based on previous average LOS (5 days, SD 1.5) the sample required to detect a difference of 1 day with 80% power was 70 patients. This study was approved by the SJGHC HREC. Results Of 163 eligible, 83 completed the questionnaire. 8 were excluded. 75 underwent analysis (50 vaccinated and 25 unvaccinated). Median age was 75 (23-83) and 63 (33-70) respectively (p< 0.01). 76% vs 48% reported >1 comorbidity (p =0.02). 10% vs 0% were admitted to ICU (p =0.16). Higher vaccination uptake was seen in older patients and those with comorbid conditions. There was a strong correlation (Spearman r= 0.54 (0.34 to 0.68, p< 0.001) between age and length of stay, but none was found between comorbidity or vaccination and length of stay. Neither age (p >0.05), comorbidity status (yes/no; p=0.99), vaccination status (p=0.61) nor any combination of these variables were significantly associated with a dichotomised outcome of acute hospital stay > 3 days. Conclusion Vaccination with the 2019 influenza vaccine had no significant effect on hospital length of stay, mortality or critical care requirement in patients admitted to hospital with influenza. Disclosures All Authors: No reported disclosures