July 15, 2020

Comparativeness effectiveness of influenza vaccines in elderly persons

Query 19-07: Comparativeness effectiveness of influenza vaccines for adults 65 years of age and older.

This research is funded by the Drug Safety and Effectiveness Network (DSEN) and conducted by the following investigators: Sasha Bernatsky, Cristiano Moura, Marina Machado and the CAN-AIM Team.

Issue:

  • Influenza respiratory infections are caused primarily by influenza A and B viruses with worldwide annual attack rate estimated at 5–10% in adults. Influenza is recognized as a cause of a broad spectrum of morbidity and mortality. In Canada, it is estimated 12,200 hospitalizations and 3,500 deaths attributable to influenza annually [1].

Study aim:

  • To determine which influenza vaccine available for adults 65 years of age and older is the most effective

Study description:

  • Vaccination is the most effective way to prevent influenza and its complications. In Canada, there are currently four types of influenza vaccines available for adults 65 years of age and older, the target population of the present project: trivalent standard dose (Agriflu®, Fluviral®, Influvac®), quadrivalent standard dose (Afluria® Tetra, Influvac® Tetra, Flulaval Tetra®, Fluzone® Quadrivalent), trivalent adjuvanted (Fluad®), and trivalent high dose (Fluzone® High-Dose).
  • The National Advisory Committee on Immunization (NACI) informs that there are insufficient head-to-head studies directly comparing efficacy, effectiveness, and immunogenicity of trivalent adjuvanted, trivalent high dose, and quadrivalent standard dose [1]. Further investigations are required to provide real-world evidence on comparative effectiveness of influenza vaccine in seniors.
  • CAN-AIM proposes a retrospective cohort study to compare the effectiveness of the above four types of influenza vaccine in adults 65 years of age and older using administrative databases from the United States.

Preliminary findings:

  • We have selected six cohorts of Medicare beneficiaries receiving influenza vaccination from 2012 until 2018 using MarketScan® databases. After applying the inclusion and exclusion criteria, we have included 211,536 adults 65 years of age and older in season 2017/2018; 368,291 in season 2016/2017; 359,188 in season 2015/2016; 417,885 in season 2014/2015; 484,341 in season 2013/2014; 533,616 in season 2012/2013. We have performed primary analyses for all six cohorts.
  • Our findings so far suggest that compared to a trivalent standard-dose vaccine, (1) trivalent high dose vaccine was more effective in preventing influenza-related events (hospitalization, ER visits, or outpatient physician visits) in seasons 2017/2018, 2015/2016, 2013/2014, and 2012/2013; (2) quadrivalent vaccine was associated with a higher risk for influenza-related outpatient physician visit in season 2014/2015; and (3) trivalent adjuvanted vaccine was associated with a higher risk for influenza-related outpatient physician visit in season 2016/2017. Comparisons with the trivalent adjuvanted vaccine were affected by the small sample size of this group and a small number of events (n=38 in 2017/2018; n=12 in 2016/2017), leading to estimates with wide 95% confidence intervals.
  • In the coming months, we will perform pooled analyses across 2012-2018, secondary analyses limited to the period of high virus circulation (up to January 31), and sensitivity analyses.  

For more information, contact: Autumn Neville, Research Coordinator. [email protected]

  1. Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2019–2020. An Advisory Committee Statement (ACS) National Advisory Committee on Immunization (NACI). Available at: https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/canadian-immunization-guide-statement-seasonal-influenza-vaccine-2019-2020.html#II2. Accessed September 26, 2019.