Background on Influenza

Influenza, an acute respiratory infection, is caused by a variety of flu viruses. The viruses spread from person to person via airborne droplets of respiratory fluids, especially after an infected individual sneezes or coughs. Flu viruses generally enter the body through the mucous membranes of the eyes, nose or mouth.

Prominent symptoms include headache, chills and a dry cough, which are followed rapidly by body aches, malaise and fever. Typically, the fever starts declining on the second or third day of the illness as upper respiratory symptoms--nasal congestion and sore throat--become more noticeable.

The viruses that cause influenza change often. Because of this, influenza vaccine is updated each year by replacing at least one of the vaccine viruses with a newer one. This is done to make sure that influenza vaccine is as up-to-date as possible.

Strains included in this year's vaccine are:

• A/New Caledonia/20/99 (H1N1)-like virus;
• A/Wisconsin/67/2005 (H3N2)-like virus (A/Wisconsin/67/2005 and A/Hiroshima/52/2005 strains);
• B/Malaysia/2506/2004-like virus (B/Malaysia/2506/2004 and B/Ohio/1/2005 strains)