410. Influence of Pre-season Antibody Titers to Influenza on Influenza Risk in a Cohort of Healthcare Personnel

Abstract

BackgroundInfluenza (flu) and other respiratory viruses circulate regularly throughout healthcare systems, often placing healthcare personnel (HCP) at high risk for illness. Hemagglutination inhibition (HAI) titers are associated with protection from flu illness, though few studies have characterized HAI in HCP. The Respiratory Protection Effectiveness Clinical Trial (ResPECT), provided HAI titers and data to assess infection risk based on four flu seasons. Participants from multiple outpatient settings wore respiratory protection within six feet of symptomatic patients.MethodsSerological samples obtained at the beginning and end of each season and anterior nasopharyngeal swabs were taken randomly and when participants reported respiratory symptoms were assessed. Our primary outcome was PCR-confirmed influenza.ResultsDuring 5,180 participant-seasons of observation, 128 PCR-confirmed influenza A infections (20 H1N1, 108 H3N2) and 34 PCR-confirmed influenza B infections. 4,041 (78%) reported receiving an annual influenza vaccine. Each log base 2 increase in titer subtype-specific titer reduced the hazard of influenza infection with A/H3N2 by 18%(Relative Risk (RR) 0.82 95% CI 0.72,0.94), by 28% for influenza B (RR 0.72 95% CI 0.56,0.92 and by 25% for influenza A H1N1 (RR 0.75 95% CI 0.57–1.0). After adjusting for HAI titers, age was not significantly associated with risk for any of the subtypes.ConclusionIn this prospective cohort of monitored HCPs, these findings support the current literature demonstrating that HAI titers are associated with protection from influenza infection. The relationship between HAI titers, influenza, and vaccination is complex, however. Vaccination was not shown to be associated with infection outcome in our model, though their effect may be difficult to separate from their effect on HAI titers.DisclosuresTrish M. Perl, MD, MSc, 7–11: Advisory Board; medimmune: Research Grant.