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

Each year, the US Influenza Vaccine Effectiveness Network estimates the effectiveness of seasonal influenza vaccine to prevent influenza-associated, medically attended acute respiratory illness.

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.

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.

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.

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