Background. During the 2012-2013 influenza season, there was cocirculation of influenza A(H3N2) and 2 influenza B lineage viruses in the United States. Methods. Patients with acute cough illness for ≤7 days were prospectively enrolled and had swab samples obtained at outpatient clinics in 5 states. Influenza vaccination dates were confirmed by medical records. The vaccine effectiveness (VE) was estimated as [100% × (1-adjusted odds ratio)] for vaccination in cases versus test-negative controls. Results. Influenza was detected in 2307 of 6452 patients (36%); 1292 (56%) had influenza A(H3N2), 582 (25%) had influenza B/Yamagata, and 303 (13%) had influenza B/Victoria. VE was 49% (95% confidence interval [CI], 43%-55%) overall, 39% (95% CI, 29%-47%) against influenza A(H3N2), 66% (95% CI, 58%-73%) against influenza B/Yamagata (vaccine lineage), and 51% (95% CI, 36%-63%) against influenza B/Victoria. VE against influenza A(H3N2) was highest among persons aged 50-64 years (52%; 95% CI, 33%-65%) and persons aged 6 months-8 years (51%; 95% CI, 32%-64%) and lowest among persons aged ≥65 years (11%; 95% CI,-41% to 43%). In younger age groups, there was evidence of residual protection from receipt of the 2011-2012 vaccine 1 year earlier. Conclusions. The 2012-2013 vaccines were moderately effective in most age groups. Cross-lineage protection and residual effects from prior vaccination were observed and warrant further investigation.
Bibliographical noteFunding Information:
Financial support. This work was supported by the CDC, through co-operative agreements with the University of Michigan (U01 IP000474), Group Health Research Institute (U01 IP000466), Marshfield Clinic Research Foundation (U01 IP000471), University of Pittsburgh (U01 IP000467), and Baylor Scott and White Health (U01 IP000473); and by the National Institutes of Health (grants UL1 RR024153 and UL1TR000005 to the University of Pittsburgh).
Potential conflict of interest. H. Q. M., M. E. S., J. K. M., and E. A. B. report receiving research grant support from Medimmune. M. G. reports receiving research support from Medimmune and Novartis. P. A. P. reports service on speakers bureau for MedImmune. R. K. Z. and M. P. N. reports research grant support from Medimmune, Sanofi Pasteur, Pfizer, and Merck and consulting fees from Medimmune. J. M. R. reports research grant support from Pfizer. S. E. O. reports research grant support from Sanofi Pasteur. A. S. M. reports receiving research grant support from Sanofi Pasteur and consulting fees from Novartis, Novavax, and GlaxoSmithKline. All other authors report no potential conflicts.
- Medically attended influenza
- Vaccine effectiveness