Vaccine effectiveness of 2011/12 trivalent seasonal influenza vaccine in preventing laboratory-confirmed influenza in primary care in the United Kingdom: evidence of waning intra-seasonal protection

R. Pebody , N. Andrews , J. Mcmenamin , H. Durnall , J. Ellis , C. I. Thompson , C. Robertson (1, 2) , S. Cottrell , B. Smyth , M. Zambon , C. Moore , D. M. Fleming , J. M. Watson

1 University of Strathclyde [Glasgow]
2 IPRI - International Prevention Research Institute

The 2011/12 season was characterised by unusually late influenza A (H3N2) activity in the United Kingdom (UK). We measured vaccine effectiveness (VE) of the 2011/12 trivalent seasonal influenza vaccine (TIV) in a test-negative case-control study in primary care. Overall VE against confirmed influenza A (H3N2) infection, adjusted for age, surveillance scheme and month, was 23% (95% confidence interval (CI): -10 to 47). Stratified analysis by time period gave an adjusted VE of 43% (95% CI: -34 to 75) for October 2011 to January 2012 and 17% (95% CI: -24 to 45) for February 2012 to April 2012. Stratified analysis by time since vaccination gave an adjusted VE of 53% (95% CI: 0 to 78) for those vaccinated less than three months, and 12% (95% CI: -31 to 41) for those vaccinated three months or more before onset of symptoms (test for trend: p=0.02). For confirmed influenza B infection, adjusted VE was 92% (95% CI: 38 to 99). A proportion (20.6%) of UK influenza A(H3N2) viruses circulating in 2011/12 showed reduced reactivity (fourfold difference in haemagglutination inhibition assays) to the A/Perth/16/2009 2011/12 vaccine component, with no significant change in proportion over the season. Overall TIV protection against influenza A(H3N2) infection was low, with significant intraseasonal waning.

Mots clés: Adolescent Adult Aged Case-Control Studies Child Confidence Intervals Female Great Britain/epidemiology Hemagglutination Inhibition Tests Humans Influenza A Virus; H3N2 Subtype/genetics/immunology/isolation & purification Influenza Vaccines/*administration & dosage/immunology Influenza; Human/diagnosis/*epidemiology/*prevention & control/virology Male Middle Aged Primary Health Care Reverse Transcriptase Polymerase Chain Reaction Seasons Sentinel Surveillance Sequence Analysis; DNA Time Factors Treatment Outcome Vaccination/statistics & numerical data

Domaines: Santé publique et épidémiologie

R. Pebody, N. Andrews, J. Mcmenamin, H. Durnall, J. Ellis, et al.. Vaccine effectiveness of 2011/12 trivalent seasonal influenza vaccine in preventing laboratory-confirmed influenza in primary care in the United Kingdom: evidence of waning intra-seasonal protection. Euro Surveill, 2013, 18 (5). ⟨hal-01261731⟩