Key flu facts

What is flu?

Influenza (flu) is an infection caused by influenza viruses. There are three types of influenza virus: A, B and C. Influenza A and B viruses cause virtually all of the clinical illness. The symptoms of influenza C infection are usually mild. Outbreaks of flu occur every year during the winter months.

The influenza virus attacks the respiratory tract (the ear, nose and throat). The virus is mainly spread by inhaling virus particles in respiratory droplets which are produced when someone with flu coughs or sneezes. It can also spread by touching respiratory droplets from another person or object and transferring these to the nose or mouth area for example when eating or grooming.

The incubation period of the virus before onset of symptoms is between one and three days. Symptoms of influenza generally last about a week during which time a person usually feels sufficiently unwell to have to spend a few days in bed. However, a cough, tiredness and general malaise may persist for two weeks or longer.

Influenza infection is different from having a cold: the symptoms of flu come on suddenly and include fever, headache, extreme tiredness and an aching body. A dry cough, sore throat and stuffy nose are other common symptoms of the infection. In young children symptoms may be less specific. While high fever, cough and running nose are present, main symptoms might be listlessness, reluctance to feed, vomiting and diarrhoea.

Although most people recover completely from flu within a few weeks, for some people the infection is more serious and leads to complications. These illnesses may require treatment in hospital and can be life-threatening especially in the elderly, people with heart or chest disease and those in poor health.

Serious complications of influenza infection

Viral pneumonia:

• Cough
• Breathing difficulties
• Chest pains
• Fever
• Headache
• Confusion

Secondary bacterial infections such as Haemophilus influenzae or Staphylococcus aureus:

• Pneumonia (cough, breathing difficulties, chest pains, fever, headache, confusion)
• Bronchitis (coughing, mucus secretion)
• Otitis Media (fever, ear pain)
• Sinusitis (facial pain, post nasal drip)

Worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

Who is most at risk from flu?

Anyone can get the flu but it is more serious for people aged 65 years and over and people of any age with a chronic medical condition, particularly chronic respiratory and cardiac disease. Young children have a greater risk of being infected because they will not have developed immunity to the virus.

When does the flu season start and end?

Influenza occurs most often in the winter months and usually peaks between December and March, although it can start earlier.

Why do the different types of flu change every year?

The structure of the influenza virus is unstable and new variations of the influenza viruses are constantly emerging. Typically each year one or two types of influenza A may be in circulation as well as an influenza B strain. Each year the composition of the flu vaccine protects against those types of influenza viruses that are most likely to be circulating in the coming winter.

Influenza vaccine composition for 2007/08 season

The strains of influenza virus recommended by WHO (World Health Organisation) to be included in the components for the 2007-08 vaccine are:

• An A/Solomon Islands/3/2006(H1N1)-like virus
• An A/Wisconsin/67/2005 (H3N2)-like virus
• A B/Malaysia/2506/2004-like virus

How common is flu?

The number of people who get flu varies from year to year depending on the severity of the circulating flu strains, but some cases occur every winter.

Flu can lead to large increases in the number of people who consult their General Practitioner (GP). During an epidemic, GP consultation rates reach 1000 per 100,000 population or over. At this rate, over 50,600 people consult their GP every week in Scotland (figure extrapolated from population). However, with the exception of the 2003/4 and 2006/7 flu seasons in most of the recent seasons GP consultation rates have rarely exceeded rates of 50 per 100,000.

Hospital admissions for respiratory disorders increase during a period of flu activity, with around 3000 people aged 65 to 74 years, and around 6000 people aged 75 years and over admitted to hospital in England each year during the flu season. It is estimated that on average, an additional 12,500 people die each year during the flu season in England and Wales, depending on the amount and severity of circulating flu.

It is difficult to establish how many people are seriously affected by flu each year in Scotland as the infection may make other illnesses worse leading to complications that may result in hospitalisation and/or death. The numbers can be estimated by comparing the number of people admitted to hospital and the number of deaths that occur during a flu epidemic with the numbers that occur in the winter weeks when flu is not in circulation. The majority of the excess deaths and hospital admissions occur in the elderly.

The Vaccine

What is flu vaccine?

Flu vaccine contains components of two types of influenza A and one type of influenza B viruses. Because the flu virus is continually changing, and different types circulate each winter, a new influenza vaccine has to be produced each year.

Can the flu vaccine cause flu?

As the viruses are inactivated and do not contain live viruses, they cannot cause flu. Some people may experience mild flu-like symptoms for up to 48 hours after immunisation as their immune system responds to the vaccine, but this is not flu.

How is the vaccine made?

The viruses for the vaccine are grown in hens eggs, then inactivated (killed) and purified before being made into the vaccine. There are currently three types of flu vaccine that are as effective as each other but differ in the way the vaccines are made. The first type is prepared by treating whole viruses with organic solvents or detergents to inactivate them (“disrupted virus” vaccines). The second type is prepared by extracting and purifying components of the influenza viruses (“surface antigen” vaccines).

The third type is prepared from disrupted virus particles reconstituted into virosomes. Other flu vaccines have been developed such as an intranasal attenuated live flu vaccine but these are not currently available in the UK.

How is the vaccine composition decided each year?

The WHO decides each February which three flu viruses are likely to be the greatest threat in the forthcoming winter season. The decision is made by analysing several thousand influenza viruses in the WHO influenza laboratories in London, Atlanta, Melbourne and Tokyo. These laboratories assess which strain has been dominant over the previous winter and look for evidence of new strains that have the potential to spread, and how well the current vaccines protect them.

When is the vaccine made?

Production of the vaccine starts in March each year after the WHO announcement and continues throughout the spring and summer for the northern hemisphere. The flu vaccine is then available in the UK from September onwards.

How effective is the vaccine?

The currently available influenza vaccines give 70-80% protection against infection with influenza virus strains closely matching those in the vaccine. In the elderly, protection against infection may be less, but immunisation has been shown to reduce the incidence of bronchopneumonia, hospital admissions and mortality.

Do people who have had flu vaccine or had flu before need to be immunised?

Yes. The viruses which cause flu change every year, which means the flu this winter is likely to be different from last winter’s, so the vaccine will be different as well.

How long does the protection from influenza vaccine last?

Protection lasts for about one year. To provide continuing protection, annual immunisation is necessary with vaccine containing the most recent strains.

When should flu vaccine be given?

The best time is between September and early November, before the main flu season. However, although people can be vaccinated until the end of March they shouldn’t leave it too late.

How soon is it before the influenza vaccine starts to work?

After immunisation, antibody levels may take up to 10-14 days to reach protective levels.

Can it be given at the same time as other vaccines?

Yes. The flu vaccine can be given at the same time as other vaccines such as pneumococcal vaccine or the routine childhood vaccines. They should be given at a separate site, preferably in a different limb. If given in the same limb, they should be at least 2.5cm apart.

Does flu vaccine contain mercury (thiomersal)?

Some flu vaccines contain thiomersal as a preservative.

Does it matter which flu vaccine is given?

The flu vaccines that are thiomersal-free are as effective as those containing thiomersal. If a thiomersal-free influenza vaccine is not available, then a thiomersal-containing vaccine should be given. The benefits of vaccination far outweigh the risks, if any, of exposure to thiomersal-containing vaccines.

For more information on thiomersal, see thiomersal factsheet at www.immunisation.nhs.uk

Who should have the flu vaccine?

Flu vaccine is offered to the following groups of people who are most at risk from the serious complications of influenza infection:

Older people
Flu vaccine should be given to all those 65 years and over.

People with serious medical conditions
Flu vaccine should be given to all those aged six months or over who have the following medical conditions:

• Chronic respiratory disease, including chronic obstructive pulmonary disease (COPD), including chronic bronchitis and emphysema
• Bronchiectasis
• Cystic fibrosis
• Interstitial lung fibrosis
• Pneumoconiosis
• Bronchopulmonary dysplasia (BPD)
• Asthma requiring continuous or repeated use of inhaled or systemic steroids or with previous exacerbations requiring hospital admission
• Children who have previously been admitted to hospital for lower respiratory tract disease

Chronic heart disease
This includes those requiring regular medication and/or follow-up for:

• Ischaemic heart disease
• Congenital heart disease
• Hypertensive heart disease (excluding uncomplicated controlled hypertension)
• Chronic heart failure.

Chronic renal disease
This includes diseases such as:

• Nephrotic syndrome
• Chronic renal failure
• Renal transplantation

Chronic liver disease
This includes:

• Cirrhosis
• Biliary artesia
• Chronic hepatitis

Chronic neurological disease
This includes those with:

• Cerbrovascular disease, principally having experienced stroke or transient ischaemic attacks
• Multiple Sclerosis and related conditions
• Hereditary and degenerative diseases of the central nervous system.

Diabetes mellitus
Including Type 1, Type 2 requiring insulin or oral hypoglycaemic drugs, and diet controlled diabetes.

Immunosuppression due to disease or treatment
Including:

• Asplenia or splenic dysfunction
• Those on or likely to be on systemic steroids for more than a month at a dose equivalent to prednisolone at 20mgs or more per day (any age) or for children under 20 kgs a dose of 1mg or more per kg per day
• HIV infection at all stages
• Patients undergoing chemotherapy leading to immunosuppression

However, some immunocompromised patients may have a suboptimal immunological response to the vaccine.

People living in residential care homes
Flu vaccine should be given to people living in long-stay residential care homes where flu is likely to spread very quickly and cause serious illness for many people living in the care home.

People who are the main carer for an elderly or disabled person 
A carer is someone who without payment provides help and support to a partner, child or neighbour, who could not manage without their help. This could be due to age, physical or mental illness, addiction or disability.

A young carer is a child or young person under the age of 18 carrying out significant caring tasks and assuming a level of responsibility for another person, which would normally be taken by an adult.

Health and social care professionals
Health and social care staff directly involved in patient care should be immunised to reduce the spread of influenza to patients, including vulnerable patients who may not be able to respond well to their own immunisation, and also to other staff within health or social care premises. Responsibility for occupational flu immunisation rests with the employer and should be provided through an occupational health service.

Why doesn’t everyone have the flu vaccine?

For most people, influenza infection is unpleasant but not usually serious and they recover within a week or two. The vaccine is only offered to those at high risk from the serious complications of flu, or those whose occupation places them at an increased risk.

Is there anyone who shouldn’t have the flu vaccine?

There are very few people who cannot receive influenza vaccine. The vaccines should not be given to those who have had a confirmed anaphylactic reaction to a previous dose of the vaccine or any component of the vaccine (including neomycin, kanamycin and gentamicin – antibiotics which may be present in tiny (trace) amounts).

The vaccines are prepared in hens eggs and should not be given to individuals with known anaphylactic hypersensitivity to egg products. If a person is ill with a fever, the immunisation should be delayed until they have recovered.

Can the influenza vaccine be given to women who are pregnant who belong to an at risk group?

Yes. Pregnant women who have medical conditions that increase their risk of complications from influenza should be vaccinated before the influenza season, regardless of the stage of pregnancy.

There is no evidence of risk from vaccinating pregnant women or those who are breast-feeding with inactivated virus vaccines. Pregnant women should preferably receive a thiomersal-free influenza vaccine. If a thiomersal-free vaccine is not available then a thiomersal-containing vaccine should be given. The benefits of vaccination far outweigh the risks, if any, of exposure to thiomersal-containing vaccines.

What adverse reactions might be seen after influenza vaccine?

Some side effects should be expected. Some people get a slight temperature and aching muscles for a couple of days afterwards and their arm may feel a bit sore where they were injected. Any other reactions are very rare.

Guillain-Barré syndrome has been reported very rarely after immunisation with influenza vaccine (one case per million people vaccinated in one US study), although a causal relationship has not been established.

What are the main reasons people give for not wanting a flu vaccine?

• Some people think that flu vaccine can actually give them flu – this is not true – the vaccine doesn’t contain any live virus, so it can’t cause flu.
• They think they don’t need to get vaccinated again if they have had the vaccine or flu before. This is wrong. Flu viruses change every year so you need a new flu vaccine each year to protect against the viruses most likely to be circulating in the coming winter.
• They think the vaccines don’t work. The currently available influenza vaccines give 70-80% protection against infection with influenza virus strains closely matching those in the vaccine. But they do not protect against other respiratory infections such as the common cold.
• They don’t like needles. On the other hand most people don’t like being laid low by flu. Even so, last year, 75% of people aged 65 years and over had their flu vaccine.

What should someone do if they catch flu?

The best way to treat flu is to stay at home and rest. It is important to drink plenty of liquids to replace the fluids lost by sweating, and eat what you can. Painkillers such as paracetamol or aspirin can be taken to relieve headache and muscle pains and to reduce a fever. Aspirin should not be given to children under 16 years of age (unless under the direction of a doctor).

Influenza is a virus, so antibiotics won’t work unless the flu has led to a bacterial illness that requires treatment. Most people recover from flu in about a week although they may feel weak for several weeks afterwards. Medical advice should be sought if symptoms become severe or last more than about a week. Those with chronic or long-standing illness may need medical attention earlier.

Can antiviral drugs be used to prevent or treat flu?

The best way to prevent flu is by vaccination before the start of the flu season. For some people who are at risk from flu but are unable to have the vaccine or if they come into contact with flu before the vaccine has had a chance to work (within the 2 weeks following vaccination), antiviral drugs can be given to prevent flu infection for a short period of time. Antiviral drugs can also be used to treat an ‘at-risk’ person who has flu. Guidance on the use of antiviral drugs is given by the National Institute for Clinical Excellence (NICE). These guidelines have been endorsed by NHS QIS and can be found on the NICE website: www.nice.org.uk

The drugs are only given when flu is known to be circulating in the community and must be started within 48 hours of exposure or onset of symptoms so they are only used during a flu epidemic. NICE have stated that these drugs are not a substitute for influenza immunisation.

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