Mid-season influenza vaccine effectiveness 2011-2012: a Department of Defense Global, Laboratory-based, Influenza Surveillance System case-control study estimate.

Mid-season influenza vaccine effectiveness (VE) was estimated using data from surveillance conducted by the Department of Defense Global, Laboratory-based, Influenza Surveillance Program at the United States Air Force School of Aerospace Medicine. Respiratory specimens from geographically diverse military members and dependents who sought medical care 2 October 2011-3 March 2012 were analyzed by viral culture and real-time reverse transcriptase-polymerase chain reaction; influenza viruses were typed and sequenced. Controls were influenza test-negative. Overall, vaccine type and subtype-specific VE were estimated using logistic regression. Adjusted VE (95% confidence interval) was: overall 77 (57-87)%; live attenuated vaccine (LAIV) 74 (48-87)%; trivalent inactivated vaccine (TIV) 75 (48-88)%. H3 component-specific VE was: overall 77 (52-89)%; LAIV 78 (47-91)%; TIV 74 (38-89)%; data were insufficient for separate H1 and B estimates. Both vaccine types showed moderate to high VE, indicating significant protection against circulating influenza strains.