What is flu?

Is an acute viral infection of the respiratory tract. Three types of influenza viruses A, B and C, with A and B responsible for most clinical illness.

Influenza is highly infectious with incubation period of one to three days usually. For most healthy people, flu is an unpleasant but usually self-limiting disease with recovery generally within a week. However, the following people are at particular risk of severe illness if they catch flu:

• Older people
• The very young especially less than six months old
• Pregnant women
• Those with underlying disease, particularly chronic respiratory, cardiac disease or chronic neurological conditions
• Those who are immunosuppressed

Influenza can present as or be complicated by bronchitis, secondary bacteria pneumonia, and in children otitis media. More usually influenza can be complicated by meningitis, encephalitis or meningoencephalitis

Flu is much worse than a heavy cold; with symptoms coming on suddenly you can experience,

• Fever
• Chills
• Headache
• Aching muscles and pain
• Extreme tiredness
• Dry cough
• Sore throat and
• Stuffy nose

Transmission

This can be through droplets, aerosols, or by direct contact with respiratory secretions of someone with the infection. It spreads rapidly, especially in closed communities. In the UK most cases occur during the winter. Don't put off getting your flu vaccination - watch this short video that shows just how easily flu can spread.

Progressive periodic changes in the protein surface of the virus result in major changes, and emergence of a new subtype. Immunity from the previous virus may not protect completely against the new subtype. With little or no immunity in the population, this may lead to widespread epidemic or even a pandemic.

What does flu mean for me?

If you're working you may have to take several days off work. For your children, a bout of flu would mean several days off school and the need to arrange childcare cover. In pregnancy it can be associated with perinatal mortality, prematurity, low birth weight and smaller size of the newborn.

How to avoid spreading and contracting flu

To reduce the risk of spreading flu:

• Wash your hands regularly with soap and warm water
• Cover your coughs and sneezes, making sure to dispose of the tissue as soon as possible
• Vaccination against seasonal influenza (flu) offers the best protection and if you are in an 'at-risk' group it is very important that you have it. If you have a long-term condition, getting the flu can put you at greater risk of developing complications that could be serious

Find out how you can help to prevent flu.

Who is eligible for the free flu vaccination?

Influenza vaccine should be offered ideally before influenza virus starts to circulate, to:

• Anyone 50 years and above
• Have certain health conditions
• Are pregnant
• Are in long-stay residential care
• Receive a carer's allowance, or are the main carer for an older or disabled person who may be at risk if you get sick
• Live with someone who is more likely to get infections (such as someone who has HIV, has had a transplant or is having certain treatments for cancer, lupus or rheumatoid arthritis)
• Frontline health or social care workers

Read further details about the children's flu vaccine on the NHS Choices website.