996. A Cluster-Randomized Trial of Adjuvanted Trivalent Influenza Vaccine vs. Standard Dose in US Nursing Homes

BACKGROUND: Pneumonia and influenza lead as vaccine-preventable infections among nursing home (NH) residents. Immunosenescence reduces vaccine response and protection from infections. More immunogenic vaccines, e.g., adjuvanted trivalent influenza vaccine [aTIV], can improve clinical outcomes. We evaluated all-cause hospitalization among long-stay NH residents offered aTIV vs. trivalent influenza vaccine (TIV). METHODS: We randomized 823 NHs within 75 miles of a Centers for Disease Control and Prevention influenza reporting city to offer one of the two egg-based influenza vaccines, aTIV or TIV, as their 2016–2017 influenza season standard of care. For the subset of long-stay NH residents (>100 days in facility as of October 1, 2016) aged ≥65 years, we determined how many were hospitalized from November 1, 2016 to June 1, 2017 on an intent-to-treat basis. We obtained all-cause hospitalization, patient-, and facility-level characteristics from Minimum Data Set and Certification and Survey Provider Enhanced Reporting data. Our primary outcome was time to first hospitalization, using Cox proportional hazards models. RESULTS: The analytic sample included 26,300 residents in 412 NHs randomized to offer aTIV and 26,474 in 410 NHs randomized to TIV. Mean age was 82.3 vs. 82.3 years, 69.3% vs. 68.6% were women, and 15.5% vs. 20.1% were African-American, for aTIV and TIV NHs, respectively. The number of residents vaccinated in the facility against influenza was 17,976 (68.3%) and 18,364 (69.4%), with an overall vaccination rate of 78.4% and 79% for aTIV and TIV NHs. Mean staff vaccination was 53.4% and 54.4% for aTIV and TIV NHs. There were 5,479 (20.8%) hospitalizations in the aTIV and 5,839 (22.1%) in TIV NHs, respectively [adjusted as prespecified, hazard ratio (HR) 0.94, 95% confidence interval (CI): 0.88, 0.99]. Post-hoc adjustment for the imbalance in race increased heterogeneity, HR 0.97, 95% CI: 0.91, 1.04. A total of 18.2% vs. 17.5% (HR 1.05, 95% CI: 0.99, 1.11) of residents in aTIV and TIV NHs died. CONCLUSION: Compared with TIV, aTIV may reduce hospitalization risk of long-stay NH residents during a predominantly A/H3N2 influenza season, despite reported reduced effectiveness due to egg-based mutagenesis of egg-based vaccines. NCT: 02882100 DISCLOSURES: S. Gravenstein, Seqirus: Consultant, Grant Investigator and Scientific Advisor, Consulting fee, Research grant and Speaker honorarium. H. E. Davidson, Seqirus: Grant Investigator and Investigator, Research grant and Research support. K. Mcconeghy, Seqirus: Investigator, Research support. L. Han, Seqirus: Investigator and Research Contractor, Research grant. D. Canaday, Seqirus: Grant Investigator, Research grant and Research support. E. Saade, Seqirus: Investigator, Research grant and Research support. R. R. Baier, Seqirus: Investigator, Research support. V. Mor, Seqirus: Investigator, Research grant and Research support.