What is Influenza?

See: Adult vaccination – a key component of healthy ageing

What is Influenza?

  • An acute respiratory disease caused by human in­fluenza viruses
  • Symptoms include fever, headache, muscle pain, runny nose, sore throat, non-productive cough and a general feeling of ill-health

Influenza Type A Virus

  • Cause of most severe disease
  • Associated with epidemics and pandemics

Other Influenza Virus Strains

  • Type B virus also contributes to epidemics
  • Novel strains occasionally develop to which humans have little immunity

Influenza is a seasonal disease in Europe, with a peak during the months from October to May. While most people recover quickly, regular seasonal epide­mics in Europe cause severe illness and death [ECDC 2013]. The high prevalence of milder forms of the disease also contributes to a substantial social and economic burden, and pressure on health services [ECDC 2013].

Seasonal influenza particularly affects high-risk groups:

  • Young people (<15 years of age)
  • Older people (>65 years of age)
  • Pregnant women
  • People with a chronic medical condition (e.g. chronic pulmonary disease, chronic cardiovascular disease)


The 2010–11 influenza season in Europe was epidemiologically important as it was the first after the pandemic in 2009 and gave some indication of the characteristics of the new interpandemic (seasonal) influenza [ECDC 2013].

  • Children frequently presented in primary care
  • Greece, Ireland, the UK and to a lesser extent Denmark and France, had a high incidence of severe disease and deaths [ECDC 2013]
  • There was considerable pressure on hospital and intensive care services [ECDC 2013]
  • Adults <65 years of age had the most severedisease (Figure 1)
    • Most had underlying medical conditions
    • In the previous interpandemic, older adults (≥65 years) with underlying conditions had the most severe disease [ECDC 2013]

Data from France can provide indications of the burden of illness to the population [Institut de Veille Sanitaire 2013].

  • More than 3.5 million people were affected
  • There were 724 serious cases requiring
    intensive care
  • Among the serious cases, only 11% were known to be vaccinated
  • There were at least 117 influenza deaths (ages ranged between 5 months and 97 years of age)

Hospitalisation [Who European Hospital Morbidity Database]
■ Hospitalisation rates peaked at 0.35 per 1000 during the pandemic year of 2009
■ The highest rates (0.87 and 1.55 per 1000) were recorded in Latvia and Lithuania, respectively

Mortality [Who Detailed European Mortality Database]
Use of reported influenza deaths to estimate influenza incidence provides comparable data over a number of countries. However, these reports probably underestimate deaths due to influenza and do not account for deaths occurring from a secondary infection (e.g. pneumonia) as a consequence of influenza.

  • Mortality rates in the EU were uniformly low in 2005 (less than 0.4 per 100,000) and during the 2009 pandemic year (around 0.25 per 100,000)

Vaccination And Control Strategies
Vaccination of high risk and other groups can
reduce the clinical and economic burden of seasonal influenza; in the US the Centers for Disease Control and Prevention (CDC) recommends that all adults be vaccinated against seasonal influenza. In Europe, ECDC notes that there is a continuing need to [ECDC 2013]:
■ Increase influenza vaccine uptake
■ Improve surveillance for development of resistance to antiviral drugs
■ Recommend influenza immunisation to the population group aged over 65 years

Influenza: Summary Of Key Points

  • Influenza is a seasonal disease, with a winter peak
  • It particularly affects the young, older people, pregnant women and those with chronic medical conditions
  • Epidemics can result in severe illness and death, significant socio-economic burden and pressure on health services
  • Mortality rates are probably underestimated
  • Influenza vaccine uptake should be increased, and is particularly recommended among older adults