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Influenza (Flu)

influenza virusInfluenza, more commonly known as the flu, is a respiratory illness, affecting the lungs and airways, and is the result of an infection caused by an influenza virus. There are three types of influenza virus, known as A, B and C.
The characteristic symptoms of flu, which usually come on suddenly, are fever, chills, headache, cough, body aches and fatigue. The flu virus is usually spread in the small droplets of saliva coughed or  sneezed into the atmosphere by an infected person. Direct contact with hands contaminated with the virus can also spread infection.
As influenza circulates each year in the UK during the winter months (October to April), it is often called seasonal flu and results from slight changes to the virus from the previous year which means that some people who encounter the new virus may no longer be fully immune.
A vaccine (the 'flu jab') is developed for each season which is offered free to everyone over 65 and people in certain 'at-risk' groups who are more likely to develop complications as a result of having flu. More information about seasonal flu is available from NHS Direct Wales.
Seasonal flu is not the same as pandemic flu. Pandemics arise when a new influenza virus emerges which is capable of spreading in the worldwide population.  The last pandemic occurred in 2009/10 when a new strain of pandemic influenza A(H1N1) (commonly called swine flu) was identified in the United States and Mexico and subsequently spread worldwide.
More information about the first flu pandemic of the 21st century is given in a separate webpage: The 2009 flu pandemic

Who gets it and how serious is it?

Anyone can get flu and the flu virus is easily passed from person to person.  Flu can spread rapidly especially in closed communities such as residential homes.
Most people recover from a bout of flu uneventfully but complications can occur particularly in the elderly or in those with certain medical conditions. These can result in serious illness and can be life-threatening.


For people who are generally fit and healthy, flu is a self limiting illness and symptoms can be treated at home using remedies commonly available from pharmacies.
Medical advice should be sought if symptoms become severe or last longer than a week. Antibiotics may be prescribed to treat any secondary bacterial infections that may develop but these are ineffective against the flu virus itself.
People in groups most at risk of complications may require medical attention earlier. GPs may prescribe antiviral medications such as Zanamivir and Oseltamivir to such patients for both the treatment and prevention of flu, following the guidelines produced by the National Institute for Health and Clinical Excellence (NICE).

How common is it?

The number of cases of seasonal flu varies from year-to-year depending on the types of flu virus in circulation and the uptake and effectiveness of the vaccine. In most years, the number of cases of flu peaks between December and March.
Flu activity is measured on the basis of the number of people for every 100,000 population who consult their GP with flu-like illness each week. This is measured using a network of Welsh volunteer ‘sentinel’ network GP practices.
In Wales, flu activity is defined as:
  • baseline (low level) activity: less than 25 consultations per 100,000 people in the population
  • normal seasonal activity: 25 -100 consultations per 100,000 people in the population
  • higher than normal seasonal activity: 100 -400 consultations per 100,000 people in the population
  • epidemic activity: more than 400 consultations per 100,000 people in the population 
Throughout the year, Public Health Wales publishes a weekly flu report for Wales which is available from the Public Health Wales Health Protection Division website from the link: Seasonal influenza surveillance data for Wales


In Wales and the UK, flu vaccination is routinely offered to people considered to be more at risk of developing complications from contracting flu. These include those who:
  • are aged 65 and over
  • are living in long-term residential or nursing homes
  • have chronic heart or chest complaint, including asthma
  • have chronic kidney or liver disease
  • have a chronic neurological condition
  • have diabetes
  • have lowered immunity due to disease or treatment such as steroid medication or cancer treatment
  • are pregnant 


Additionally, health workers and carers and members of a recognised voluntary organisation who provides planned emergency first aid at organised public events and members of Welsh Ambulance Service Trust community first responder scheme providing first aid directly to the public are also offered vaccination against flu.
In Wales from 1 September 2013 the first phase will commence of a childhood flu vaccination programme for all children aged 2 – 16 years.
For the 2013-14 flu season, a vaccine will be offered to:
  • all children aged 2 and 3 years on 1 September 2013 (i.e. children with a date of birth from 2 September 2009 to 1 September 2011) through GPs
  • all children in school year 7 primarily through school health services. More information is available from the webpage Childhood Influenza Vaccination Programme 2013-14.
Gradual implementation of the programme to include all children aged 2-16 years is expected to follow over subsequent years.
Flu vaccines contain killed or weakened flu viruses, selected by the World Health Organisation (WHO) on the basis of the viruses seen to be circulating by their collaborating laboratories.

Minimising impact in Wales

Public Health Wales undertakes enhanced influenza surveillance during the flu season and data collected is compiled into weekly influenza reports which are available for both health professionals and the public.
This enhanced influenza surveillance enables levels of circulating flu activity in the community and the strains of flu virus in circulation to be established. This information is used to aid decision-making with regard to the use of antivirals and enables predictions on hospital emergency bed requirements to be made.
The most effective method of controlling influenza is by maintaining high levels of immunisation among vulnerable groups or whole populations. Public Health Wales contribute to this through the work of the Vaccine Preventable Disease Programme (VPDP) and Local Health Protection Teams (HPTs). These support WAG in setting a strategic direction for immunisation services, support LHBs in managing local services and achieving targets, and support General Practice and Trusts delivering services. 
In addition Public Health Wales identify and follow up local cases and outbreaks of influenza to prevent spread of the disease amongst vulnerable people.
Through the VPDP, Public Health Wales facilitates the sharing of innovative approaches to delivering flu immunisation, assesses impact of interventions and campaigns to increase uptake of flu immunisation and monitors and reports on flu vaccine uptake each winter. 

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Last updated: 24 September 2013