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Chief Medical Officer

Bird flu and pandemic influenza: what are the risks?

Last modified date:

30 June 2008

A severe form of avian influenza or 'bird flu' – called H5N1 – has affected poultry flocks and other birds in several countries since 2003. As of 30 June 2008, 385 people have also caught the infection, as a result of close and direct contact with infected birds. Two hundred and forty-three of these have subsequently died. There is no firm evidence that H5N1 has acquired the ability to pass easily from person to person. However, concerns remain that the virus might develop this ability, or that it might mix with human flu viruses to create a new virus. It is this ability of avian influenza, to change and to mix, that has given rise to the fear of a new human flu pandemic. This regularly updated feature explains the background to the disease, and assesses the nature of the risk to people living in the UK.

Latest news

Outbreaks of H5N1 in the UK

There have been a small number of incidents of highly pathogenic avian influenza in wild birds or poultry in the UK since 1959, most recently in Dorset.

There have also been some incidents of low pathogenic avian influenza.

For details of the latest situation and general advice please see the Defra and HPA websites.

What is bird flu?

Avian influenza or 'bird flu' is a highly contagious disease of birds, caused by influenza A viruses. In birds, the viruses can present with a range of symptoms from mild illness and low mortality to a highly contagious disease with a near 100% fatality rate.

The bird flu virus currently affecting poultry and some people in Asia and other areas is the highly pathogenic H5N1 strain of the virus.

As the virus can remain viable in contaminated droppings for long periods, it can be spread among birds, and from birds to other animals, through ingestion or inhalation.

All bird species are thought to be susceptible to avian influenza. Migratory birds such as wild ducks and geese can carry the viruses, often without any symptoms of illness, and show the greatest resistance to infection. Domestic poultry flocks, however, are particularly vulnerable to epidemics of a rapid, severe and fatal form of the disease.

There are many different subtypes of influenza A virus. The most virulent are called highly pathogenic avian influenza (HPAI) and can reach epidemic levels among birds. Of these, subtype H5, and more particularly subtype H5N1 currently, pose the greatest concern for human health. Two other subtypes - H9 and H7 - have caused illness in people but neither has caused outbreaks in poultry as severe as H5N1-related ones.

According to the World Health Organization (WHO), there is mounting evidence that the H5N1 strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in people.

Factsheet on avian influenza (Defra) (opens new window)

The current outbreak in birds

The outbreak of avian influenza of most concern to health experts is H5N1. It began in poultry in South Korea in mid-December 2003, and has affected birds in many countries in Asia, Europe, Middle East and Africa. It involves a variant of the same virus subtype as that associated with the 1997 Hong Kong outbreak.

EU and UK controls are in place aimed at preventing the spread of bird flu. Nonetheless, it remains a remote possibility that bird flu could be introduced to poultry through the migration of wild birds, the illegal importation of dead chickens for consumption, the illegal importation of live birds or the entry into the UK of a person who has acquired the illness in an infected area.

The Food Standards Agency provides more detailed information about imports and bird flu. The World Organization for Animal Health (OIE) maintains an up-to-date list of countries affected.

Article 2.7.12.4. of the OIE Terrestrial Animal Health Code (2005) states that a country may regain its status as an avian influenza-free country three months after “a stamping-out policy (including disinfection of all affected establishments) is applied, providing that surveillance in accordance with Appendix 3.8.9. has been carried out during that three-month period”.

How can bird flu infect people?

H5N1 is able to infect people because it is able to cross the species-barrier, although it does not do this easily. In human populations, where domestic pigs and wild and domestic birds live in close proximity with people, the mingling and exchange of human and animal viruses can more easily occur. Those who have become infected have had close direct contact with infected birds.

Human infection with avian influenza viruses usually causes mild conditions such as conjunctivitis (eye infection) and mild flu-like symptoms, with one notable exception, the highly pathogenic H5N1 virus. More severe infection can lead to pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.

Avian influenza in birds and humans (WHO) (opens new window)

Person-to-person transmission

There are no confirmed cases of person to person spread in the recent outbreak. So far, while some instances of spread from one person directly to another have been reported, these have been isolated one-off occurrences with no further spread to people, and the route of transmission remains unconfirmed.

Outbreaks of bird flu affecting people

Until mid-December 2003 — the start of the current outbreak in poultry — highly pathogenic avian influenza (HPAI) was considered a rare disease of birds.

The first documented cases in people appeared in Hong Kong in 1997, when 18 people infected with an H5N1 virus strain were admitted to hospital, six of whom died. The source of infection in most cases was traced to contact with diseased birds on farms and in live poultry markets.

As of 30 June 2008, 385 reported cases of H5N1 infection in people have occurred in fourteen countries, Thailand, Vietnam, Cambodia, Indonesia, China, Turkey, Iraq, Azerbaijan, Egypt, Djibouti, Nigeria, Laos and most recently Myanmar and Pakistan. Two hundred and forty-three of these have been fatal.

Regularly updated information about human cases of H5N1 is available on the WHO website.

Advice to travellers

WHO does not at present recommend any restrictions on travel to any country currently experiencing outbreaks of bird flu in poultry flocks, including countries which have also reported cases in humans.

If you are visiting countries with reported outbreaks of H5N1 bird flu among poultry, you should observe the following measures:

do not visit bird or poultry farms or markets
avoid close contact with live or dead poultry
do not eat raw or poorly-cooked poultry or poultry products, including blood
wash your hands frequently with soap and water
do not attempt to bring any live birds or poultry products back to the UK.

Countries currently known to have cases of H5N1 in birds, or where they have had cases and surveillance is still ongoing, are:

Afghanistan
Bangladesh
Benin
Cambodia
Cameroon
China (including Tibet and Hong Kong)
Egypt
India
Indonesia
Iran
Iraq
Japan
Korea (Rep. of)
Laos
Pakistan
Russia (Kaluzhskaya Oblast, Krasnodarskiy Kray, Moskovskaya Oblast and Respublika Adygeya, Rostovskaya Oblast and Primorskiy Kray)
Saudi Arabia
Switzerland
Thailand
Turkey
Ukraine
Vietnam

Avian influenza in other animals

It is possible, although rare, for other animals such as cats to become infected with the H5N1 virus. However, there have been no reports of H5N1 avian influenza virus ever having been transmitted to humans from animals other than domestic poultry.

Defra provides information about the risks to other animals of H5N1 infection.

Avian influenza and other animals (Defra) (opens new window)

Guidance on handling and disposing of dead garden and wild birds

This joint guidance produced by the Department of Health and Defra applies in all circumstances where members of the public may come across a dead bird, regardless of whether there is any bird flu in the UK.

Guidance on handling and disposing of dead garden and wild birds (opens new window)

Risk of a human influenza pandemic

Photo showing how viruses can be spread from person to person

"We do not know what the virus is that will cause pandemic 'flu. What we do know is that Mother Nature has the recipe book and its just a matter of time before she starts cooking." Sir Liam Donaldson speaking at the launch of his 2005 Annual Report, at the Royal College of Pathologists, Carlton Terrace, London, 21 July 2006.

"Wherever in the world a flu pandemic starts, perhaps with its epicentre in the Far East, we must assume we will be unable to prevent it reaching the UK. When it does, its impact will be severe in the number of illnesses and the disruption to everyday life. The steps we are setting out today will help us to reduce the disease's impact on our population."
Sir Liam Donaldson, Chief Medical Officer, 1 March 2005

But what is a pandemic, and what causes it?

We are used to epidemics of 'ordinary' flu, which occur seasonally, every year, around the world. An epidemic is a widespread outbreak of disease occurring in a single community, population or region.

A pandemic, on the other hand, occurs on a much greater scale, spreading around the world and affecting many hundreds of thousands of people across many countries.

Three influenza pandemics occurred in the last century - 1918 to 1919 (Spanish flu), 1957 to 1958 (Asian flu) and 1968 to 1969 (Hong Kong flu). All affected large numbers of the population, causing many deaths and huge economic and social disruption.

There are three main groups of flu viruses: influenza A, B and C. Influenza B and C viruses infect people only, however, influenza A viruses have the ability to cross the species barrier and infect people, birds, and animals such as pigs and horses. Among people, influenza A is the source of most 'ordinary' flu epidemics and has caused all previous flu pandemics.

Experts fear that the H5N1 subtype of avian influenza A could trigger the next pandemic, for several reasons. Firstly, it has already demonstrated an ability to infect people and cause severe disease - one of the key characteristics of a pandemic strain. Secondly, the virus has the ability to mutate and acquire genes from viruses infecting other species.

Experts are concerned that the virus could either:

adapt, giving it greater affinity for humans, or;
exchange genes with a human flu virus, thereby producing a completely new virus strain capable of spreading easily between people, and causing a pandemic.

Alternatively the pandemic could arise from a strain of influenza A unrelated to H5N1.

By necessity, if a pandemic strain were to occur then few people, if any, would have a natural immunity to it.

The World Health Authority (WHO) has developed a global alert system, based on six pre-defined phases, as a way of signalling the seriousness of the risk of an influenza pandemic. The world is presently at phase 3, where a new influenza virus subtype is causing disease in humans, but is not yet spreading efficiently and sustainably among humans.

What can be done?

The DH website provides detailed information on what the Government is doing to plan for an influenza pandemic. The UK has had a national influenza pandemic plan since 1997 and was one of the first countries to publish such a plan.

The UK Influenza Pandemic Contingency Plan, published in 2005, has now been replaced by Pandemic Flu: A national framework for responding to an influenza pandemic published on 22 November 2007.

In addition to the Framework are a series of documents covering specific areas such as: strategic and operational planning guidance for adult social care, hospitals, ambulance services and community health care settings; and an ethical framework designed to assist clinicians and others in developing policies on clinical issues for use during a pandemic.

The Framework and its accompanying documents provides information that will enable all organisations to continue to develop and improve their response and service/ business continuity plans.

The new clinical countermeasures outlined in the Framework have been strengthened to offer protection should the ‘worst case scenario’ take place, which it is anticipated could affect up to 50 per cent of the population.

“The UK is still in the vanguard of countries worldwide in preparing for a pandemic, and is also one of the leading global players in addressing the cross-sectoral issues in their planning.”
Dr David Heymann, Assistant Director-General - Health Security and Environmant, World Health Organization

Pandemic flu: A national framework for responding to an influenza pandemic

Antiviral drugs

Three antiviral drugs are licensed in the UK for the treatment of influenza; oseltamivir (Tamiflu), zanamivir (Relenza) and amantadine (Symmetrel).

These drugs work by reducing the ability of the virus to spread within the body. They reduce the level and severity of symptoms and may prevent the development of complications.

Scientific advice is that Tamiflu and Relenza are suitable for stockpiling because their safety profile is good and the virus is less likely to develop resitance to these products.

However, Tamiflu is easier to use (an oral capsule or solution) than Relenza (administered with an inhaler) and has been more widely stockplied globally.

Amantadine is not recommended for stockpiling as there are major problems with resistance and it has a range of side effects.

The Government currently has enough courses of Tamiflu to treat 25 percent of the population. Deliveries were completed in September 2006.

The Government plans to increase this stock, sufficient to be able to treat 50 percent of the population.

Pandemic Flu: A national framework for responding to an influenza pandemic

Vaccines

H5N1 vaccine

The Department of Health is currently stockpiling 3.3 million doses of H5N1 vaccines. These may be used in frontline healthcare workers if there was a close enough match between the vaccine strain and the emerging pandemic strain.

Whether this vaccine will be suitable for use against a new pandemic flu strain will very much depend on how much the pandemic strain may have mutated and changed from the original H5N1 virus strain used to create the vaccine.

Vaccine technology is a fast moving field and the Department is monitoring the development of new prepandemic vaccines carefully.

It is possible that a future influenza pandemic may be caused by a strain of influenza which is not H5N1 related.

If the virus should change substantially, it is unlikely that the existing vaccine would be effective, and a new one would have to be developed.

Pandemic flu vaccine

In addition to the H5N1 vaccine stockpile, DH has signed an Advanced Supply Agreement for enough pandemic flu vaccine to treat the entire UK population, in the event that a pandemic should occur.

The proposal to purchase the capacity needed to make pandemic flu vaccine, in advance, will ensure that an effective vaccine is available for use as quickly as possible after a flu pandemic starts.

Because of the time required to identify the virus and manufacture vaccine, it is expected that the first stocks would be available around three to six months after the pandemic strain has been identified and made available by the World Health Organisation.

Interim advice to other organisations

Expanded information and advice aimed at local authorities, schools and other education establishments, essential services and the business sector, and on restrictions on travel, has also been included in the new Framework.

Further guidance will be issued by Health Departments based on the advice of the UK National Influenza Pandemic Committee, guidance from the WHO, or real time modelling, when and should the need arise.

If there was a flu pandemic, what could I do?

You can reduce, but not eliminate, the risk of catching or spreading influenza during a pandemic by:

covering your nose and mouth when coughing or sneezing, using a tissue when possible;
disposing of dirty tissues promptly and carefully – bag and bin them;
avoiding non-essential travel and large crowds whenever possible;
maintaining good basic hygiene, for example washing your hands frequently with soap and water to reduce the spread of the virus from your hands to your face, or to other people;
cleaning hard surfaces (e.g. kitchen worktops, door handles) frequently, using a normal cleaning product;
making sure your children follow this advice.

If you do catch flu:

stay at home and rest;
take medicines such as aspirin, ibuprofen or paracetemol to relieve the symptoms (following the instructions with the medicines). Please note: Children under 16 must not be given aspirin or ready made flu remedies containing aspirin;
drink plenty of fluids.
Contact your doctor if your condition worsens. (Advice on symptoms and signs to watch for will be publicised when a pandemic starts.)

These measures are for your own health and to avoid spreading the illness to others.

Should a flu pandemic occur, more information will be given at the time through leaflets, websites and the media. Such information will tell you how you can protect yourself and your family and what to do if you think you are infected.

Some people will be recommended treatment – further information will be given at the time.

How to keep up-to-date

In addition to the specific webpages listed above, the following links are to websites (and website sections) that provide useful and regularly updated information on avian influenza.