Influenza Vaccine Effectiveness in the 2011–2012 Season: Protection Against Each Circulating Virus and the Effect of Prior Vaccination on Estimates

• Published in: Clinical infectious diseases 2014-02, Vol.58 (3), p.319-327
• Main Authors: Ohmit, Suzanne E., Thompson, Mark G., Petrie, Joshua G., Thaker, Swathi N., Jackson, Michael L., Belongia, Edward A., Zimmerman, Richard K., Gaglani, Manjusha, Lamerato, Lois, Spencer, Sarah M., Jackson, Lisa, Meece, Jennifer K., Nowalk, Mary Patricia, Song, Juhee, Zervos, Marcus, Cheng, Po-Yung, Rinaldo, Charles R., Clipper, Lydia, Shay, David K., Piedra, Pedro, Monto, Arnold S.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; and Commentaries; ARTICLES AND COMMENTARIES; Biological and medical sciences; Child; Child, Preschool; Female; H3N2 subtype influenza A virus; Health status; Human viral diseases; Humans; Immunization; Inactivated vaccines; Infant; Infectious diseases; Influenza; Influenza A virus; Influenza vaccines; Influenza Vaccines - administration & dosage; Influenza Vaccines - immunology; Influenza, Human - epidemiology; Influenza, Human - prevention & control; Influenza, Human - virology; Male; Medical records; Medical sciences; Middle Aged; Orthomyxoviridae - classification; Orthomyxoviridae - isolation & purification; Polymerase chain reaction; Preventive medicine; Real-Time Polymerase Chain Reaction; Regression analysis; Research grants; Respiratory diseases; Reverse Transcriptase Polymerase Chain Reaction; Treatment Outcome; United States - epidemiology; Vaccination - methods; Vaccines; Viral diseases; Viral diseases of the respiratory system and ent viral diseases; Viral vaccines; Viruses; Young Adult
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1093/cid/cit736

Background. Each year, the US Influenza Vaccine Effectiveness Network examines the effectiveness of influenza vaccines in preventing medically attended acute respiratory illnesses caused by influenza. Methods. Patients with acute respiratory illnesses of ≤7 days' duration were enrolled at ambulatory care facilities in 5 communities. Specimens were collected and tested for influenza by real-time reverse-transcriptase polymerase chain reaction. Receipt of influenza vaccine was defined based on documented evidence of vaccination in medical records or immunization registries. Vaccine effectiveness was estimated in adjusted logistic regression models by comparing the vaccination coverage in those who tested positive for influenza with those who tested negative. Results. The 2011–2012 season was mild and peaked late, with circulation of both type A viruses and both lineages of type B. Overall adjusted vaccine effectiveness was 47% (95% confidence interval [CI], 36–56) in preventing medically attended influenza; vaccine effectiveness was 65% (95% CI, 44–79) against type A (H1N1) pdm09 but only 39% (95% CI, 23–52) against type A (H3N2). Estimates of vaccine effectiveness against both type B lineages were similar (overall, 58%; 95% CI, 35–73). An apparent negative effect of prior year vaccination on current year effectiveness estimates was noted, particularly for A (H3N2) outcomes. Conclusions. Vaccine effectiveness in the 2011–2012 season was modest overall, with lower effectiveness against the predominant A (H3N2) virus. This may be related to antigenic drift, but past history of vaccination might also play a role.