title: Mid-season real-time estimates of seasonal influenza vaccine effectiveness in persons 65 years and older in register-based surveillance, Stockholm County, Sweden, and Finland, January 2017.
abstract: Systems for register-based monitoring of vaccine effectiveness (VE) against laboratory-confirmed influenza (LCI) in real time were set up in Stockholm County, Sweden, and Finland, before start of the 2016/17 influenza season, using population-based cohort studies. Both in Stockholm and Finland, an early epidemic of influenza A(H3N2) peaked in week 52, 2016. Already during weeks 48 to 50, analyses of influenza VE in persons 65 years and above showed moderately good estimates of around 50%, then rapidly declined by week 2, 2017 to 28% and 32% in Stockholm and Finland, respectively. The sensitivity analyses, where time since vaccination was taken into account, could not demonstrate a clear decline, neither by calendar week nor by time since vaccination. Most (68%) of the samples collected from vaccinated patients belonged to the 3C.2a1 subclade with the additional amino acid substitution T135K in haemagglutinin (64%) or to subclade 3C.2a with the additional haemagglutinin substitutions T131K and R142K (36%). The proportion of samples containing these alterations increased during the studied period. These substitutions may be responsible for viral antigenic change and part of the observed VE drop. Another possible cause is poor vaccine immunogenicity in older persons. Improved influenza vaccines are needed, especially for the elderly.
authors.affiliation: Department of Communicable Disease Control and Prevention, Stockholm County Council, and Karolinska Institutet, Department of Medicine Karolinska Solna, Unit of Infectious Diseases, Stockholm, Sweden.|These authors contributed equally to this work.
authors.forename: Maria-Pia
authors.initials: MP
authors.lastname: Hergens
authors.affiliation: These authors contributed equally to this work.|Impact Assessment Unit, Department of Public Health Solutions, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Baum
authors.affiliation: Unit for laboratory surveillance of viral pathogens and vaccine preventable diseases, Department of Microbiology, The Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Mia
authors.initials: M
authors.lastname: Brytting
authors.affiliation: Viral Infections Unit, Department of Health Security, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Niina
authors.initials: N
authors.lastname: Ikonen
authors.affiliation: Viral Infections Unit, Department of Health Security, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Anu
authors.initials: A
authors.lastname: Haveri
authors.affiliation: Unit for laboratory surveillance of viral pathogens and vaccine preventable diseases, Department of Microbiology, The Public Health Agency of Sweden, Solna, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Wiman
authors.affiliation: These authors contributed equally to this work.|Vaccination Programme Unit, Department of Health Security, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Nohynek
authors.affiliation: Department of Communicable Disease Control and Prevention, Stockholm County Council, and Karolinska Institutet, Department of Medicine Karolinska Solna, Unit of Infectious Diseases, Stockholm, Sweden.|These authors contributed equally to this work.
authors.forename: Åke
authors.initials: Å
authors.lastname: Örtqvist
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005387:Finland; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000517:prevention & control* / Q000821:virology*; D008297:Male; D010802:Phylogeny; D011159:Population Surveillance; D016016:Proportional Hazards Models; D060888:Real-Time Polymerase Chain Reaction; D012141:Respiratory Tract Infections / Q000517:prevention & control / Q000821:virology; D012621:Seasons; D017678:Sex Distribution; D013548:Sweden; D016896:Treatment Outcome; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D007252:Influenza Vaccines
keywords: Finland; Sweden; influenza; influenza virus; surveillance; viral infections