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What's the influenza vaccine (flu vaccine)?

Vaccination is the principal measure for preventing influenza and reducing the impact of epidemics. Various types of influenza vaccines have been available and used for more than 60 years. They are safe and effective in preventing both mild and severe outcomes of influenza. The vaccine is made by purifying proteins from three different strains of the influenza virus. Because influenza viruses are continuously mutating to avoid our immune systems, new vaccines are made up every

year. To remain protected from the influenza virus you need the new vaccine each year. Protection develops about 2 weeks after receiving the vaccine. All current inactivated influenza vaccines contain trace levels of egg protein and should not be used by individuals with egg protein allergies.

Each season's flu vaccine contains three virus strains that are the most likely to be encountered in the coming flu season. When there is a good match between the anticipated flu strains and the strains used in the vaccine, the vaccine is 70-90% effective in people under 65. Because immune response diminishes somewhat with age, people over 65 may not receive the same level of protection from the vaccine, but even if they do contract the flu, the vaccine diminishes the severity and helps prevent complications. The virus strains used to make the vaccine are inactivated and will not cause the flu. In the past, flu symptoms were associated with vaccine preparations that were not as highly purified as modern vaccines, not to the virus itself. In 1976, there was a slightly increased risk of developing Guillain-Barré syndrome, a very rare disorder, associated with the swine flu vaccine. This association occurred only with the 1976 swine flu vaccine preparation and has never recurred. Constant genetic changes in influenza viruses mean that the vaccines' virus composition must be adjusted annually to include the most recent circulating influenza A(H3N2), A(H1N1) and influenza B viruses.

It is recommended that elderly persons, and persons of any age who are considered at “high risk” for influenza-related complications due to underlying health conditions, should be vaccinated. Among the elderly, vaccination is thought to reduce influenza-related morbidity by 60% and influenza-related mortality by 70-80%. Among healthy adults the vaccine is very effective (70-90%) in terms of reducing influenza morbidity, and vaccination has been shown to have substantial health-related and economic benefits in this age group. The effectiveness of influenza vaccine depends primarily on the age and immunocompetence of the vaccine recipient and the degree of similarity between the viruses in the vaccine and those in circulation. Influenza vaccination can reduce both health-care costs and productivity losses associated with influenza illness.

The WHO's Global Influenza Surveillance Network writes the annual vaccine recipe. The network, a partnership of 112 National Influenza Centres in 83 countries, is responsible for monitoring the influenza viruses circulating in humans and rapidly identifying new strains. Based on information collected by the Network, WHO recommends annually a vaccine that targets the 3 most virulent strains in circulation.

More information on influenza (flu)

What is influenza (flu)? - Influenza (flu) is a respiratory infection caused by one of the influenza viruses that typically is spread by air or by direct contact.
How is influenza transmitted? - Influenza is spread through contact with droplets from the nose and throat of an infected person during coughing and sneezing.
What causes influenza? - The flu is caused by three types (strains) of viruses - influenza A, B and C. Influenza A is responsible for the deadly influenza pandemics.
What's the influenza virus? - The influenza virus is in a class of viruses known as orthomyoxoviruses, with myxo referring to the fact that they infect mucus membranes.
What're the risk factors for influenza? - All people 50 years of age and older are at increased risk for serious illness with the flu, or in contact with those at high risk, and should receive vaccine.
What're the complications of influenza? - Influenza complications usually arise from bacterial infections of the lower respiratory tract. Pneumonia is the major serious complication of influenza.
What are the symptoms of influenza? - Influenza can cause a variety of symptoms. Typical flu symptoms include headache, fever, chills, cough and body aches. Intestinal symptoms are uncommon.
How is influenza diagnosed? - Diagnosis of influenza (flu) is based on typical symptoms of fever, chills, headaches, cough and body aches. There are a variety of tests to detect influenza.
What is the treatment for influenza? - The main treatment for influenza (flu) is to rest adequately, drink plenty of fluids, and avoid exertion. Amantadine and rimantadine are effective against influenza A.
How to control or prevent influenza? - The preferred treatment for influenza, and most viral infections is prevention. The prevention can be achieved through vaccinations.
What's the influenza vaccine (flu vaccine)? - Vaccination is the principal measure for preventing influenza. Influenza vaccinations are given to millions annually.
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All information is intended for reference only. Please consult your physician for accurate medical advices and treatment. Copyright 2005,, all rights reserved. Last update: July 18, 2005