What is influenza?
Influenza (flu) is an illness caused by the flu virus. There are different strains of flu virus. Flu is passed from person to person through droplets created when someone with the infection sneezes or coughs. You can also catch it by touching a surface where the virus has been deposited. Flu can spread quickly in these ways.
Symptoms of flu include a high temperature (fever), muscle aches, cough, headache and extreme tiredness. Flu usually lasts for between two and seven days. Most people recover fully. Complications such as a chest infection or pneumonia develop sometimes.
Complications are more common in young babies, older people, people with an underlying disease (especially heart or lung diseases), pregnant women and people who have a weak immune system. Complications are sometimes serious and a number of people die each year in the UK. These are usually elderly.
There are three types of flu virus – A, B and C. Influenza types A and B cause most of the cases of flu. Each winter a different strain of the flu virus causes an outbreak which affects many people. This is called seasonal flu. During an outbreak of seasonal flu, if you get a flu-like illness, it is more likely to be caused by the prevailing flu virus than by any other. Most cases of flu usually occur in a period of six to eight weeks during the winter.
Swine flu is caused by a particular strain of influenza A virus which is called influenza virus A (H1N1v). It seems to affect children and young adults more commonly than those over the age of 60 years. Most people with this type of influenza have a mild flu-like illness. You are more likely to have sickness and/or diarrhoea with this type of flu. This type of flu virus caused the pandemic in 2009/10. It is also thought likely to be around this winter (2011/12).
Note: bird flu (avian influenza) is different and is more serious.
Immunisation against seasonal flu
Flu immunisation (the flu jab) gives excellent protection against seasonal flu and lasts for one year. If 10 people have the flu jab, it will provide protection from flu for 7 or 8 of them.
The immunisation is normally given in October or November each year. It is made from the strain of flu virus that is expected in the coming winter. Each year this is slightly different, so a new jab needs to be made every year. You need a yearly jab to stay protected.
Flu jabs do not prevent other viral infections which can cause coughs, colds and flu-like illnesses. It protects only against the particular flu virus that is expected in the coming winter.
The immunisation does not actually contain any living flu virus. This means that it cannot cause flu or any other infections. If you develop a cough or cold shortly after having a flu immunisation it is a coincidence.
Who should be immunised against the seasonal flu virus?
Seasonal flu is the particular type of flu virus that arrives in the UK each autumn. The actual type varies from year to year. The new jab is developed each year to protect against the expected type. This year (2011-2012), the flu jab will also provide protection against the influenza A viral H1N1v strain (swine flu). It takes up to 14 days for full protection after having the jab.
The Department of Health (DH) issues advice as to whom should be immunised. This is reviewed from time to time. The aim is to protect people who are more likely to develop complications from flu. Current advice is that you should be immunised against the seasonal flu virus each autumn if you:
- Are aged 65 or over.
- Have any chronic (ongoing) lung diseases.
Examples include chronic bronchitis, emphysema, cystic fibrosis and severe asthma (needing regular steroid inhalers or tablets). It is also recommended for any child who has previously been admitted to hospital with a chest infection.
- Have a chronic heart disease.
Examples include angina, heart failure or if you have ever had a heart attack.
- Have a serious kidney disease.
Examples include nephrotic syndrome, kidney failure, a kidney transplant.
- Have a serious liver disease such as cirrhosis.
- Have diabetes.
- Have a poor immune system.
Examples include if you are receiving chemotherapy or steroid treatment (for more than a month), if you have HIV/AIDS or if you have had your spleen removed.
- Have certain serious diseases of the nervous system such as multiple sclerosis or have had a stroke in the past.
- Live in a nursing home or other long-stay residential care accommodation.
In addition to the main at-risk groups of people listed above:
- You should be immunised if you are the main carer for an elderly or disabled person whose welfare may be at risk if you fall ill with flu.
- Staff involved in direct patient care (including nursing and care homes) may be offered a flu jab from their employer.
- Pregnant women. Even if you are otherwise healthy it is now recommended that all pregnant women receive the flu jab.
If you are healthy and aged under 65 and you do not fall into any of the above categories, then you do not need immunisation against seasonal flu. This is because you are unlikely to develop complications from flu.
Why do pregnant women need to have the flu jab?
Pregnant women are at increased risk of developing a more severe illness. They are also more likely than nonpregnant women to be admitted to hospital. There are no known problems from giving seasonal flu jab to women who are pregnant.
Are there any side-effects from seasonal flu jab?
Immunisation against the seasonal influenza virus usually causes no problems. You may have a temporary mild soreness at the injection site. Sometimes, it can cause a mild fever and slight muscle aches for a day or so. This soon settles and does not lead to flu or other problems.
Serious reactions have been reported but are rare. For example, a severe allergic reaction, inflammation of nerves and inflammation of the brain are very rare reactions.
Who should not have the seasonal flu jab?
The vast majority of people can receive the flu immunisation. However, the following groups of people should not be immunised:
- If you are have a severe allergy to eggs. However, you can still receive a different immunisation that protects against the influenza A viral (H1N1v) strain.
- If you have had a previous allergic reaction to a flu virus immunisation in the past.
The flu immunisation can be given at the same time as other immunisation; it is often given at the same time as the pneumonia immunisation. It is also safe to be given if you are either pregnant or breast-feeding.
Further sources of information
References and Disclaimer | Provide feedback
- The influenza immunisation programme 2010/11, Chief Medical Officer, Dept of Health, June 2010
- Key vaccine information: Seasonal flu, Dept of Health, January 2011
- Immunizations – seasonal influenza, Prodigy (September 2011)
- Tamma PD, Ault KA, del Rio C, et al; Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol. 2009 Dec;201(6):547-52. Epub 2009 Oct 21. [abstract]
- Jamieson DJ, Honein MA, Rasmussen SA, et al; H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009 Aug 8;374(9688):451-8. Epub 2009 Jul 28. [abstract]