Flu season and living with HIV

October 2007     View PDF     En español

What is the flu?

The flu virus is quite common, highly contagious and very prone to changing itself. There are three categories of flu viruses: type A, B and C. All three can change into new strains, though type A mutates often and causes most of the illness in the US.

Two important proteins on the surface of the virus readily change, or mutate. These are called haemagglutinin (H) and neuraminidase (N). Strains of type A are named by the different versions of these proteins. For example, the avian flu virus is called H5N1, because it has haemagglutinin 5 and neuraminidase 1 on its surface.

You cannot develop a lifelong immunity to influenza. Even if you are protected against a flu virus one year, you may not be protected from a new strain the next year.

The flu virus originates in birds and often infects pigs, where it mutates into new strains. This is why new flu shots are required each year. Most Americans get flu shots in October and November. However, the flu season can last as late as May, so getting vaccinated later is a wise choice for some.

Each year researchers try and predict the most likely strains of influenza to hit the US. Sometimes, different strains show up rather than what was predicted. Depending on how serious an illness they produce, new vaccines may be rushed into production. For 2007–2008, the vaccines for the following three strains are available:

• Type A: Solomon Islands/3/2006 (H1N1)-like (new for this season);
• Type A: Wisconsin/67/2005 (H3N2)-like; and
• Type B: Malaysia/2506/2004-like antigens.