Influenza Vaccine Effectiveness in the United States During the 2016–2017 Season

BACKGROUND: Each year, the US Influenza Vaccine Effectiveness Network estimates the effectiveness of seasonal influenza vaccine to prevent influenza-associated, medically attended acute respiratory illness. METHODS: Patients aged ≥6 months seeking outpatient medical care for an acute respiratory illness within 7 days of illness onset were enrolled in 5 study locations during the 2016–17 influenza season. Specimens were collected and tested for influenza by RT-PCR. Patients were considered vaccinated if they received ≥1 dose of any seasonal influenza vaccine ≥14 days before illness onset, according to medical records, immunization registries and self-report. Interim vaccine effectiveness (VE) estimates were calculated as 100% x (1 – adjusted odds ratio) from multivariable logistic regression models comparing odds of vaccination among influenza-positive vs. influenza test-negative patients. RESULTS: From November 28, 2016—April 14, 2017, 7,410 patients were enrolled; 2,073 (28%) tested influenza-positive, including 1,419 (68%) influenza A (1,364 [96%] A/H3N2) and 649 (31%) influenza B viruses. Interim overall adjusted VE was 43% (95% confidence interval [CI], 37–49) against medically attended illness due to any influenza virus; interim VE estimates were 38% (95% CI, 29–45) against A/H3N2 and 54% (95% CI, 45–62) against any influenza B virus. Antigenic characterization indicated that circulating viruses remained similar to vaccine strains. CONCLUSION: Preliminary results for the 2016–17 season showed significant protection against medically attended influenza due primarily to A/H3N2 and B viruses. Preliminary results for A/H3N2 and B viruses were consistent with previous seasons in which circulating viruses were antigenically similar to vaccine strains. Final results are pending. DISCLOSURES: A. S. Monto, sanofi pasteur: Grant Investigator, Research grant; Novartis: Consultant, Consulting fee; Protein Sciences: Consultant, Consulting fee; E. T. Martin, Merck: Grant Investigator, Research grant; Roche: Grant Investigator, Research grant; E. Belongia, MedImmune: Grant Investigator, Research support; H. Q. Mclean, MedImmune: Grant Investigator, Research grant; M. Gaglani, MedImmune: Grant Investigator, Research grant; R. Zimmerman, Merck: Grant Investigator, Research grant; sanofi pasteur: Grant Investigator, Research grant; Pfizer: Grant Investigator, Research grant; M. P. Nowalk, Merck: Grant Investigator, Research grant; L. A. Jackson, Novavax: Grant Investigator, Research grant