by Alison Bowler

Created on: May 03, 2009

Influenza is often perceived as a minor infection and many people do not bother getting a flu shot. It is not a mild inconvenient infection it is in fact potentially fatal. Between 20000 and 40000 deaths are attributed to flu and its complications annually in the United States. Even without complications an influenza infection may mean up to two weeks of work while being ill and recovering.

The receiving of a flu shot before the start of the flu season can prevent the infection. In the Northern hemisphere this shot is normally given in September as the flu starts to appear in October with a peak of infection from January to March.

The flu shot contains inactive protein subunits of viral particles. These proteins are antigenic which means they are capable of inducing an immune response. It is this immune response that produces antibodies which will help protect the vaccinated person against the Influenza.

The influenza shot must be given every year to maintain immunity. Each year the strains of circulating virus changes slightly. These slight changes, known as antigenic drift, means that a new formulation of vaccine is required. In addition the immunity induced by vaccination is short lived and the level of antibodies produced may not be at a protective level a year after receiving the shot.

Some people express concerns over side effects from the vaccine. Early vaccines were made from killed virus that had been grown in fertile hens' eggs. These impure vaccines could lead to side effects particularly in persons allergic to eggs. Today the use of purified viral subunits which have been extracted from recombinant viruses provides a much safer vaccine.

There is also a belief that it is possible to catch the flu from vaccination. Through most of the world the vaccine used contains no live virus so it is impossible to catch the flu from such a shot. Russia uses a vaccine made of a live attenuated virus. Attenuation reduces the ability of the virus to cause infection.

It is possible to catch the flu even having been given a flu shot. Scientists monitor cases of influenza from around the world to try and ensure the best possible vaccine is made available each year. At times the vaccine may not be effective as a new strain of influenza virus may evolve at any time. It takes time to include this new strain within the vaccine formulation. This does not happen often and the vaccine will still prevent infection from any other circulating viral strains. Also totally new strains

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