title: Retrospective public health impact of a quadrivalent influenza vaccine in the United States.
abstract: BACKGROUND
  Vaccination is an effective preventive strategy against influenza. However, current trivalent influenza vaccines (TIVs) contain only one of the two influenza B lineages that circulate each year. Vaccine mismatches are frequent because predicting which one will predominate is difficult. Recently licensed quadrivalent influenza vaccines (QIVs) containing the two B lineages should address this issue. Our study estimates their impact by assessing what would have been the US public health benefit of routinely vaccinating with QIV in 2000-2013.
  
  
  METHODS
  We developed a dynamic compartmental model that accounts for interactions between influenza B lineages (natural or vaccine-induced) and simulates the multiyear influenza dynamics for 2000-2013. Age-structured population dynamics, vaccine efficacy (VE) per strain, and weekly ramp-up of vaccination coverage are modeled. Sensitivity analyses were performed on VE, duration of immunity, and levels of vaccine-induced cross-protection between B lineages.
  
  
  RESULTS
  Assuming a cross-protection of 70% of the VE of the matched vaccine, the model predicts 16% more B lineage cases prevented by QIV. Elderly (≥65 years) and young seniors (50-64 years) benefit most from QIV, with 21% and 18% reductions in B lineage cases. Reducing cross-protection to 50%, 30%, and 0% of the VE of the matched vaccine improves the relative benefit of QIV to 25%, 30%, and 34% less B lineage cases.
  
  
  CONCLUSIONS
  Using a dynamic retrospective framework with real-life vaccine mismatch, our analysis shows that QIV routine vaccination in the United States has the potential to substantially reduce the number of influenza infections, even with relatively high estimates of TIV-induced cross-protection.
authors.affiliation: EHESP Rennes, Sorbonne Paris-cité, Paris, France.|Aix-Marseille Univ, UMR EPV Emergence des Pathologies Virales-190, Marseille, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Crépey
authors.affiliation: Unit of PharmacoEpidemiology & PharmacoEconomics (PE2), Department of Pharmacy, University of Groningen, Groningen, The Netherlands.
authors.forename: Pieter T
authors.initials: PT
authors.lastname: de Boer
authors.affiliation: Unit of PharmacoEpidemiology & PharmacoEconomics (PE2), Department of Pharmacy, University of Groningen, Groningen, The Netherlands.|Institute of Science in Healthy Aging & health caRE (SHARE), University Medical Center Groningen (UMCG), University of Groningen, Groningen, The Netherlands.
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Postma
authors.affiliation: ICON Clinical Research, Oxford, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Pitman
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D056738:Cross Protection; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009981:Influenza B virus / Q000235:genetics / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000737:chemistry; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008004:Licensure; D008297:Male; D008875:Middle Aged; D018448:Models, Immunological; D011634:Public Health; D012189:Retrospective Studies; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Dynamic model; influenza; quadrivalent influenza vaccine; trivalent influenza vaccine; vaccine effectiveness; vaccines