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Immunisation and Vaccines

Influenza

Further Information

Additional information relating to influenza, including current seasonal surveillance reports, can be found in the respiratory section of this website.

Causative Agent

Influenza Virus

Clinical Description

Influenza is an acute viral infectious disease, characterised by the sudden onset of fever, cough, malaise, headache and myalgia.

Transmission

Transmission is by inhalation of infected aerosols/droplets. Spread can occur very rapidly in the community and especially in hospital and institutional settings.

Surveillance in Scotland

Virus laboratories report confirmed isolates and serological diagnoses to HPS. Real time monitoring of flu like illness as reported by volunteer GP spotter practices has in the past provided the most reliable indicator of the extent of influenza activity, and is used to derive rates of illness in the population as a whole. An extrapolated consultation rate of over 1000 cases per 100,000 in any one week denotes an epidemic. Winter 2000 - 2001 saw the introduction of SERVIS (Scottish Enhanced Respiratory Viral Infection Surveillance).SERVIS is an integrated approach to influenza surveillance, which offers a more detailed and accurate picture of the influenza outbreak during the winter season. The main component of SERVIS is the provision of clinical data from sentinel computerised general practices with linked virological testing in a small sample of consultations from each practice.

Trends in Scotland (1995-2001)

As with the rest of the UK and other parts of Europe Scotland experienced a moderately severe influenza outbreak in the winter of 99/2000, with rates of consultation exceeding 800 per 100,000. In contrast the winter season of 2000/01, which has just come to an end, saw the mildest flu activity since records began in 1972, although SCIEH (now HPS) did receive significant numbers of laboratory reports of influenza type B virus especially toward the end of the season (see Figure 1 and Figure 2 below).

Evidence from SERVIS, which for the first time provided information on the age groups consulting their GP for flu and other respiratory illness, suggested that suspected flu cases were mainly being seen in the middle age ranges, a feature consistent with a season where the circulating virus is predominantly B. The winter seasons of 1995/96 and 1996/97 were relatively mild and predominantly caused by influenza A.

Incidence and Risk

5 - 10 % of the population are affected by influenza each year during seasonal winter outbreaks. This can rise to 20% and over in epidemic years, the last of which occurred in 1989/90. Most at risk from complications are the elderly and individuals with underlying cardio-respiratory illness.

Prevention

The most effective means of prevention against flu is inactivated flu vaccine, which is specifically tailored to the likely viruses in circulation each season. The vaccine is currently recommended for those aged 65 and over and other at risk individuals, as well as key health and social services employees.

Current Research / Study Groups

In its first year of operation (for the winter season 2000/01), the Scottish Enhanced Respiratory Viral Surveillance (SERVIS) scheme has recruited 37 practices, which participate in the Continuous Morbidity Recording scheme. In addition to reporting detailed age and sex breakdowns of consultations for respiratory illness including influenza, they also undertake a limited number of throat swabs for laboratory analysis. The Scottish Executive also provided additional funding to SCIEH (now HPS) for 2000/01 to monitor the uptake of influenza vaccine directly in GP practices.

Flu Spotter Data - Background

The Scottish Flu spotter scheme collates reports of flu-like illness each year and currently involves 90 practices in 12 Health Board areas covering a total of 10% of the Scottish population. It is part of a group of an early warning systems operating throughout Europe, which contribute data from clinical consultations and laboratory tests to the European Influenza Surveillance Scheme (EISS). The European scheme seeks to collect data over a minimum period of week 40 to week 20 of the following year (roughly October to May). This long season allows for the surveillance of unusually early or late outbreaks, and the measurement of background levels of activity allows direct comparisons to be made between countries. The benefits of the scheme include facilitation of healthcare and disease control planning, as well as furthering our understanding of the epidemiology of influenza, which is of particular interest with the ever-present threat of an international flu pandemic arising in the future.

Threshold Value System: In order to help describe levels of influenza activity in Scotland, a system of threshold values was introduced in 1996 to describe the levels of influenza activity during a flu season. Based on the data from the GP spotter Practice Scheme, three threshold values were introduced to describe influenza activity in relation to the numbers of new cases in any one week per 100,000 of the population:

  • Baseline activity is defined as < 50 cases / 100,000
  • Normal flu season activity at between 50-600 cases / 100,000
  • Higher than normal' at between 600 and 1000 cases / 100.000
  • 'Epidemic' level at over 1000 cases / 100,000