Influenza surveillance system

THL monitors the prevalence and variation of influenza viruses in several ways, including

  • based on laboratory samples 
  • using the National Infectious Diseases Register
  • monitoring primary healthcare visits owing to influenza-like illnesses (ILIs) 
  • monitoring excess mortality during the influenza season.

As influenza viruses vary constantly, the viruses included in the influenza vaccine must be adjusted to the prevailing forms. This ensures the efficacy of the influenza vaccine. 

THL monitors the variation of influenza viruses by examining specimens of discharge from respiratory tracts collected at outpatient clinic sentinel sites and hospitals’ intensive care units.
Health centre visits owing to influenza (in Finnish)

Purpose of surveillance

  • To identify the start of an influenza epidemic and obtain up-to-date information on its progress.
  • To keep track of the genetic and antigenic variation of epidemic influenza viruses compared to the vaccine viruses.
  • To collect epidemic influenza viruses and submit them to the World Health Organization (WHO) for use in vaccines.
  • To monitor the drug resistance development of influenza viruses.
  • To identify unusual, new influenza viruses and epidemics caused by them.
  • To monitor serious influenza infections requiring intensive care and to identify factors that predispose patients to severe diseases.
  • To assess the disease burden of influenza virus infections, or morbidity and mortality.
  • To assess the efficacy of the influenza vaccine.