Swine flu (H1N1) 


Background: the 2009 swine flu pandemic

Swine flu became a pandemic in 2009 before it died down in spring 2010. A pandemic means a disease that spreads around the globe.

The virus was first identified in Mexico in April 2009. It spread quickly from country to country because it was a new type of flu virus that few people had full resistance to.

Flu pandemics are a natural event that occur from time to time. During the last century, there were flu pandemics in 1918, 1957 and 1968, when millions of people died across the world.

The 2009 swine flu virus proved to be relatively mild and the pandemic was not as serious as originally predicted. As in other countries, most cases reported in the UK were mild. Only a small number led to serious illness and sometimes death, and these were mostly in patients with existing health problems, such as cancer, that had already weakened their immune systems.

Swine flu is the common name given to a relatively new strain of influenza (flu) that caused a flu pandemic in 2009-2010.

It is also referred to as H1N1 influenza (because it is the H1N1 strain of virus).

From now on, these pages will refer to the illness as H1N1 flu.

Current status

On 10 August 2010, the World Health Organization (WHO) declared that the H1N1 influenza pandemic was officially over.

However, it is important not to ignore H1N1 flu.

The H1N1 flu virus will be one of the main viruses circulating this winter. Therefore, the H1N1 flu virus has been included in the 2010-11 seasonal flu vaccine.


It is recommended that people in high-risk groups be vaccinated against H1N1 (swine flu). This includes all pregnant women, at any stage of pregnancy.

Pregnant women in high-risk groups and those not in high-risk groups are advised to take the seasonal flu jab, which protects against H1N1 flu.

This is because there is good evidence that all pregnant women are at increased risk from complications if they catch H1N1 flu. For more information, see Advice for pregnant women.

Until now, only pregnant women in high-risk groups were advised to take the seasonal flu vaccine. For general information about flu, see the Health A-Z topics about Seasonal flu and the Seasonal flu jab

What to do if you have H1N1 flu

People with H1N1 flu typically have a fever or high temperature (over 38C or 100.4F) and may also have aching muscles, sore throat or a dry cough (see Symptoms of swine flu). The symptoms are very similar to other types of seasonal flu. Most people recover within a week, even without special treatment.

If you think you have H1N1 flu and are worried, contact your GP. They will decide the most appropriate action to take.

The National Pandemic Flu Service no longer operates.

High-risk groups 

Some people are more at risk of complications if they catch flu. People are particularly vulnerable if they have:

  • chronic (long-term) lung disease
  • chronic heart disease
  • chronic kidney disease
  • chronic liver disease
  • chronic neurological disease (neurological disorders include motor neurone disease, multiple sclerosis and Parkinson's disease)
  • immunosuppression (whether caused by disease or treatment)
  • diabetes mellitus

Also at risk are:

  • patients who have had drug treatment for asthma in the past three years
  • pregnant women
  • people aged 65 and over

See H1N1 flu - Prevention for a full list of people advised to have this year's flu jab.

To stop the virus spreading

The most important way to stop flu spreading is to have good respiratory and hand hygiene. This means sneezing into a tissue and quickly putting it in a bin. Wash your hands and work surfaces regularly and thoroughly to kill the virus.

Anyone who is concerned about flu symptoms should contact their GP, who will determine the most appropriate action to take.

  • show glossary terms
An epidemic is a sudden outbreak of disease that spreads through a population in a short amount of time.


Last reviewed: 04/01/2011

Next review due:


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