Pandemic flu

This factsheet is for people who would like information about pandemic flu.

A pandemic is a worldwide outbreak of a disease that affects many people in different countries. An influenza, or flu, pandemic happens when a new type of flu virus spreads easily and quickly across the world.

Published by Bupa’s Health Information Team, May 2011.



About pandemic flu

A flu virus is classed as a pandemic when:

  • a new type of the flu virus develops
  • most people have no immunity against the virus – this means they may not be able to fight the infection
  • humans are affected and can pass the flu virus on to others
  • the virus spreads quickly and easily around the world
An epidemic is when more people are affected by a disease than usual. A pandemic is a worldwide epidemic.

Pandemic flu is similar to seasonal flu – the normal type of flu that tends to happen at around the same time every year – but the symptoms can be more severe. This is because few people will be able to fight off the infection easily, as it is significantly different to previous strains of flu they have had.

More people are infected with the flu virus during a pandemic than are affected by seasonal flu. Seasonal flu tends to affect people in the winter, but pandemic flu can happen at any time of the year.

In the twentieth century there have several flu pandemics, including the Spanish flu outbreak in 1918 and 1919 that killed millions of people around the world. In 2009 there was a flu pandemic of the H1N1 flu virus (swine flu).

It’s difficult to predict when a pandemic will happen, which virus might cause it or how many people might be affected. Pandemic flu can affect anyone, even the fit and healthy.


The proteins that make up the flu virus are constantly changing (mutating). A flu pandemic can occur if there is a more dramatic change to the flu virus than is normally seen every year. This can happen if there is a mix of types of flu from different species, such as birds or pigs, with a human strain of flu. This is called an antigenic shift. This mix of different viruses can make a new, unique virus that no one will be immune to.

Flu viruses are very infectious. Most people catch flu by breathing in air that has the virus in it. This usually happens when people with flu cough or sneeze, which spreads the virus in the air.

You can also catch flu through direct contact with someone who has it, for example by shaking hands or by touching something they have touched. If you pick up the flu virus on your hands and then touch your nose or mouth, you may infect yourself. The flu virus can live on hard surfaces for up to 24 hours and on soft surfaces for about 20 minutes.

If you have flu, you are infectious and can spread the virus to other people, from the day when your symptoms start to five days afterwards. Children are infectious for longer.

Complications of pandemic flu

Healthy adults usually recover completely from seasonal flu in a few weeks. However, when pandemic flu develops it’s difficult to know how severe the infection will be or how it may affect people. This is because the virus is new. Some groups of people may be affected more than others.

The complications of flu can include:

  • conditions that affect your lungs, for example, pneumonia and bronchitis
  • worsening of chest conditions such as asthma
  • middle ear infections
  • inflamed sinuses (sinusitis)
Young children can sometimes have seizures or fits called febrile convulsions. These are caused by their high body temperature.

Symptoms and diagnosis

Symptoms and diagnosis

Symptoms of pandemic flu

When you catch flu, it usually takes two to three days for your symptoms to show.

Pandemic flu usually causes the same type of symptoms as seasonal flu. Flu viruses grow in the soft, warm surfaces of your nose, throat, sinuses, airways and lungs, so this is where you usually get the symptoms. The symptoms of flu include:

  • a fever (high temperature between 39ºC and 40ºC)
  • a blocked or runny nose
  • sneezing
  • headache
  • sore throat
  • cough
  • chills
  • aching muscles
  • feeling tired
  • being sick
  • diarrhoea
Symptoms usually last for about a week, but you may feel tired for a few weeks.

If you have symptoms of flu, you usually only need to see a doctor if your symptoms get worse or last for longer than a week, or if you are pregnant or have a health problem such as diabetes or heart disease. However, in the event of a flu pandemic, local government health authorities may issue different advice about when you should see a doctor in order to access appropriate treatment and prevent spread of the virus. Follow local government advice about what you should do.

Diagnosis of pandemic flu

In the event of a pandemic, you should follow local government advice about when to seek help from a doctor in order to access appropriate treatment.

Treatment and prevention

Treatment and prevention

Treatment of pandemic flu

Usually, most people who have flu can treat the symptoms themselves without needing to see a doctor.


If you have flu, there are a number of things you can do at home to help reduce your symptoms.

Drink enough fluids to prevent dehydration – at least six to eight glasses a day.
Stay at home and rest.
Take over-the-counter painkillers such as paracetamol (acetaminophen), aspirin or ibuprofen.
Always read the patient information leaflet that comes with your medicine and if you have any questions, ask a pharmacist for advice. If your child is under 16 years old, don’t give him or her aspirin or any medicines containing aspirin.


Antiviral medicines are sometimes used to treat flu during a pandemic. However, until a flu pandemic starts, doctors can't be sure that antiviral medicines will work with that particular flu virus.

Antiviral medicines can't stop you getting flu, but they may reduce your symptoms and the length of time you’re ill. Antiviral medicines work best if you take them within 48 hours of your symptoms starting.

Antiviral medicines are normally only given to people who are at risk of severe illness if they catch flu, or to healthcare workers who care for those who are ill. Availability and use of different treatments may vary from country to country. Ask your doctor for advice on your treatment options.

Antibiotics won't help with flu symptoms, as they only work on bacterial infections.

Prevention of pandemic flu

Pandemic flu can't be prevented, but there are a number of things you can do to reduce the spread of the virus and your risk of catching it. Some of the main ones are listed below.

Cover your nose and mouth with a tissue when you cough or sneeze.
Put used tissues into the bin as soon as you can.
Wash your hands with soap and water frequently.
Clean hard surfaces like door handles and desks frequently.
Stay away from large crowds of people.
Don’t travel unless it's necessary.
Have the currently recommended flu vaccine if you are in a risk group, once it becomes available.
If you have flu then wearing a face mask may help to prevent you from passing it on to someone else. However, if you don’t have flu then wearing a face mask is unlikely to prevent you catching it.

Make sure that your children follow these guidelines too.

Vaccines for pandemic flu

Vaccines are always available for seasonal strains of flu, but when a pandemic begins, it usually takes several months to make a new vaccine. In a pandemic flu period, check local government advice to find out if a vaccine is available, and whether you are eligible to receive it. Vaccines are sometimes only given to certain risk groups such as people aged over 65, and those with underlying diseases such as chronic lung disease, heart disease, diabetes and cancer. This may vary from country to country.




  • Pandemic preparedness. World Health Organization. www.who.int, accessed 25 January 2011
  • Pandemic flu. Department of Health. www.dh.gov.uk, published 2005
  • H5N1 (2009) pandemic archive. Health Protection Agency. www.hpa.org.uk, accessed 30 March 2011
  • Frequently asked questions on influenza. Health Protection Agency. www.hpa.org.uk, published January 2011
  • Seasonal Influenza. Clinical Knowledge Summaries. www.cks.nhs.uk, published August 2009
  • Frequently asked questions on pandemic influenza. Health Protection Agency. www.hpa.org.uk, published August 2008
  • The use of face masks during an influenza pandemic. Department of Health. www.dh.gov.uk, published August 2007
  • Seasonal influenza factsheet. Department of Health. www.dh.gov.uk, published 25 January 2011
  • Avian flu. Health Protection Agency. www.hpa.org.uk, published August 2008
  • Asia and Oceania. Foreign and Commonwealth Office. www.fco.gov.uk, published January 2011

Further information

World Health Organization www.who.int

This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. This content was compiled by Bupa based on clinical information and practice current as at the stated date of publication. Content is likely to reflect clinical practice in a particular geographical region (as indicated by the sources cited) – accordingly, it may not reflect clinical practice in the reader’s country of habitation. This content is intended for general information only and does not replace the need for personal advice from a qualified health professional. Photos and videos are only for illustrative purposes and do not reflect every presentation of a condition.

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