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In Europe, all available influenza vaccines are inactivated vaccines made of killed virus. Some vaccines that are recommended for the elderly contain an adjuvant (MF59). Vaccines are produced in embryonated hens’ eggs and contain three influenza virus strains: an A(H3N2), an A(H1N1) and a type B strain, which correspond to the currently circulating types and subtypes of influenza viruses. The vaccine composition is updated on a yearly basis following the recommendations made by the World Health Organization (WHO). This is based on the comparative analysis, by the four WHO Collaborating Centres on influenza (London, Atlanta, Melbourne and Tokyo), of the viruses circulating around the world collected by the global network of laboratories.

Upon vaccination, antibodies against each of the three components of the influenza vaccine will develop and provide protection against influenza by neutralising the virus. Consequently, influenza is prevented or the illness is less severe.

Vaccines are usually given as a preventive measure. Currently available viral vaccines are usually made from killed virus that stimulate an immune response to the virus. When immunized, the body is then poised to fight or prevent infection more effectively. Antivirals are drugs that may be given to help prevent viral infections or to treat people who have been infected by a virus. When given to treat people who have been infected, antiviral medications may help limit the impact of some symptoms and reduce the potential for serious complications, especially for people who are in high-risk groups.

Antivirals may help prevent infection in people at risk and lessen the impact of symptoms in those infected with influenza. A number of antiviral medications are approved to treat and sometimes prevent flu. At this time, Tamiflu® and Relenza® are the most likely antivirals to be used in a pandemic. There are efforts to find new drugs and to increase the supply of antivirals. If everyone follows the recommended uses of antivirals there will be more available for those who need it most.

The vaccination is recommended for those at high risk of serious complications from influenza. These include those aged over 65, adults and children with underlying chronic medical conditions (e.g. cardiac, pulmonary, renal diseases), diabetics and immune-compromised individuals (e.g. by HIV infection or steroid treatment). Vaccination is also recommended for individuals who are in contact with people at high risk of serious influenza complications (e.g. healthcare workers) as well as for women in the third trimester of pregnancy.

People who do not belong to the high-risk groups will also benefit from influenza vaccination.

In the Northern Hemisphere, the best time to be vaccinated is from mid-September to November. This will ensure protection before the beginning and for the duration of the annual epidemic circulation of influenza viruses, which usually occurs from November through to April.

The vaccination is the most effective means to prevent influenza. Effectiveness of the vaccination varies with the age and immune status of the vaccinated person, the (sub)type of the virus, the degree of similarity between the vaccine and the circulating virus strains and the length of time from vaccination to exposure to influenza virus. It is about 70–90% effective in healthy persons under 65 years old and usually lower among the elderly and those with chronic medical conditions. Among the high-risk groups, influenza vaccination has been shown to be most effective in preventing severe illness, secondary complications and deaths related to influenza.

Possible side effects are usually mild and can include a local reaction at the injection site (soreness, redness or swelling) and low grade fever or muscle aches that may last for a few days. Very rarely, allergic reactions can occur among people with severe allergy to eggs, as the viruses used in the vaccine are grown in hens’ eggs. The possibility of a very rare association (one in one million vaccinees) with Guillain-Barré Syndrome has been suggested. As a precautionary measure, vaccination is generally not advised for women in their first trimester of pregnancy and for children <6 months old.

Influenza viruses are highly variable and change from year to year. Therefore, it is possible to get influenza several times during a lifetime and become infected with the same virus (sub)type. The immunity provided by natural infection or vaccination with a given influenza virus strain does not necessarily provide protection against a newer virus strain. That is why the influenza vaccine composition is updated every year to include currently circulating virus strains.

Upon influenza vaccination, it takes about 2 weeks for antibodies to develop and provide immune protection against influenza. Therefore, the vaccination should be given before the start of the influenza season.

It is possible, especially among older adults, to get influenza even after being properly vaccinated. However, for those infected after vaccination, the disease is less severe and less likely to result in hospitalisation or death. In addition, influenza-like illness can be due to infection by other respiratory viruses against which the influenza vaccination does not offer protection.