Intraseason decline in influenza vaccine effectiveness during the 2016 southern hemisphere influenza season: A test-negative design study and phylogenetic assessment

Vaccine. 2019 May 1;37(19):2634-2641. doi: 10.1016/j.vaccine.2019.02.027. Epub 2019 Apr 2.


Background: We estimated the effectiveness of seasonal inactivated influenza vaccine and the potential influence of timing of immunization on vaccine effectiveness (VE) using data from the 2016 southern hemisphere influenza season.

Methods: Data were pooled from three routine syndromic sentinel surveillance systems in general practices in Australia. Each system routinely collected specimens for influenza testing from patients presenting with influenza-like illness. Next generation sequencing was used to characterize viruses. Using a test-negative design, VE was estimated based on the odds of vaccination among influenza-positive cases as compared to influenza-negative controls. Subgroup analyses were used to estimate VE by type, subtype and lineage, as well as age group and time between vaccination and symptom onset.

Results: A total of 1085 patients tested for influenza in 2016 were included in the analysis, of whom 447 (41%) tested positive for influenza. The majority of detections were influenza A/H3N2 (74%). One-third (31%) of patients received the 2016 southern hemisphere formulation influenza vaccine. Overall, VE was estimated at 40% (95% CI: 18-56%). VE estimates were highest for patients immunized within two months prior to symptom onset (VE: 60%; 95% CI: 26-78%) and lowest for patients immunized >4 months prior to symptom onset (VE: 19%; 95% CI: -73-62%).

Discussion: Overall, the 2016 influenza vaccine showed good protection against laboratory-confirmed infection among general practice patients. Results by duration of vaccination suggest a significant decline in effectiveness during the 2016 influenza season, indicating immunization close to influenza season offered optimal protection.

Keywords: Case-control study; Influenza; Influenza vaccines; Test-negative design; Vaccine effectiveness.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Case-Control Studies
  • Comorbidity
  • Female
  • Humans
  • Immunogenicity, Vaccine
  • Influenza A Virus, H3N2 Subtype / immunology
  • Influenza A virus / classification
  • Influenza A virus / immunology
  • Influenza B virus / immunology
  • Influenza Vaccines / immunology*
  • Influenza, Human / epidemiology
  • Influenza, Human / prevention & control*
  • Male
  • Middle Aged
  • Phylogeny
  • Research Design
  • Seasons*
  • Vaccination
  • Young Adult


  • Influenza Vaccines