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Flu, or influenza to give it its full name, is a highly infectious and potentially serious viral infection that affects the upper airways and lungs.

Flu or a cold?

The symptoms of flu can be similar to those of the common cold, and many people incorrectly refer to a heavy cold as flu. However, the symptoms of a cold appear gradually, are not severe and tend to affect just your nose and throat. The symptoms of flu are more severe, causing fever and aching muscles and you will not be able to do your usual activities.

Flu is usually more common in the winter months. In the UK, the ‘flu season’ roughly lasts from September to April. There are vaccines available that can protect against flu, you can check whether you should have the flu vaccination, Find out whether you should have the flu vaccination

Flu symptoms

Seasonal flu can give you any of these symptoms:

  • sudden fever (a temperature of 38°C/100.4°F or above)
  • dry, chesty cough
  • headache
  • tiredness
  • chills
  • aching muscles
  • limb or joint pain
  • diarrhoea or stomach upset
  • sore throat
  • runny or blocked nose
  • sneezing
  • loss of appetite
  • difficulty sleeping

Although most healthy people usually recover in a week or so, flu can leave you feeling tired and ‘out of sorts’ for a while afterwards. Flu can, however, lead to serious medical complications, especially in the elderly and people with underlying medical conditions. 

Babies and small children with flu may also appear drowsy, unresponsive and floppy.

Symptoms will usually peak after two to three days and you should begin to feel much better within five to eight days. A cough and general tiredness may last for two to three weeks.

New strains of flu

Flu can be very dangerous, even for young and healthy people, particularly when a new type develops and nobody has any immunity to it. When this happens the infection can spread very rapidly around the world and many millions of people can be affected and deaths can occur. This is called a pandemic.

The names given to different types (‘strains’) of flu viruses are related to the area and year in which the new type was first found – names like ‘Asian flu 1957’ or ‘Spanish flu 1918’.

Epidemics and pandemics

Flu is usually more common in the winter months. When a large number of people get the flu then an epidemic occurs – in the UK this is defined as when more than 400 out of every 100,000 of the population consult their doctor about flu or flu-like symptoms per week. If a large proportion of the world population catches a strain of flu and which spreads very rapidly, it is known as a pandemic. The flu may then cause a high number of deaths even among people who would not normally be seriously affected it.

In 1918, the Spanish flu pandemic killed more fit and healthy young men than the First World War itself, and caused the death of up to 40 million people worldwide. Since then, there have been two more flu pandemics, one in 1957/58 and another in 1968/69, although these were not so severe.

Avian (‘bird’) flu

Avian influenza, or ‘bird flu’ is a type of virus that is contagious in birds – particularly poultry. Avian flu does not usually affect other species other than birds, and sometimes, pigs. However, occasionally, certain strains of avian flu can infect humans. There is no evidence that avian flu spreads from human to human, but can be caught through close contact with infected birds.

Swine flu

A strain of flu called H1N1, which is more commonly known as 'swine flu', has caused concern because it is a new variant of flu that has passed from pigs to man to become a human flu virus. This means that it can pass from human to human and has led to infection rates in some parts of the world now qualifying as pandemic levels with most people having little immunity to it.

A number of deaths from swine flu were reported in Mexico, where it was first found, however, most cases reported in the UK proved to have relatively mild symptoms.

Although in August 2010, the World Health Organization declared that the swine flu (H1N1) pandemic was over, it did not go away. Therefore, it is important that those people considered to be at high risk, including people with certain chronic illnesses and pregnant women, should be vaccinated against it.

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