WHAT IS THE FLU: The flu is caused by the influenza virus, which targets the respiratory tract by binding to the surface of cells. Then the virus releases its genetic information into the cell's nucleus to replicate itself. When the cell dies, those copies are released into the body, infecting other cells. Flu symptoms are unpleasant, but not life-threatening by themselves. However, the flu weakens the immune system, making the body vulnerable to more serious infections, such as pneumonia. Because the flu is caused by a virus -- as opposed to bacteria -- antibiotics are not an effective treatment. Both the flu and the common cold are best treated by bed rest, consuming lots of fluids, and taking over-the-counter medication to ease symptoms until the virus runs its course.
HURDLES TO EFFECTIVE VACCINES: There are three basic strains of the flu virus: A, B and C. A is the most common strain, and the most severe. The flu vaccine works by triggering the body's immune system response. The body recognizes the vaccine as a foreign invader and produces antibodies to it. However, flu strains differ from year to year. A phenomenon called original antigenic sin occurs when the antibodies produced by the body's immune system to fight exposure to the flu virus become part of the body's "memory" so that it can fight off future exposure to the same flu strain. The problem is that those same antibodies end up suppressing the creation of new antibodies when the body is exposed to a new strain of the flu, making last year's flu vaccine ineffective against the newer strain. The phenomenon has also been observed in dengue fever and HIV, among other viruses.