A couple of years ago an epidemic of bird flu panic swept across the US. Fear of a pandemic that could kill millions of humans spread from Asia to Australia, Britain, Italy, Poland, and other countries, including the US and Canada.

Scientists know that two dangerous bird flu viruses, known as H5 and H7, have modified their behavior enough to transmit the disease from poultry and other birds to human beings. What they don't know is when the virus will mutate so that it can be transmitted from human to human.

That submicroscopic biochemical event could rock the world.

If that happens, only the proper type and dose of vaccine given at the right time along with careful personal hygiene will be effective in fighting off the disease.

Does that mean that millions will die? Nobody knows, because the characteristics of the human form of the virus haven't been observed. It could end up being nothing more than a mild discomfort. Or it could be lethal. More likely it will be somewhere between with the elder, the infirm, and the ill being especially vulnerable to its death-dealing potential.

Supplies of the anti-flu pill known as Tamiflu have disappeared from the shelves in many countries, although the Swiss pharmaceutical company Roche recently announced plans to increase yearly production of the pills from 50 million to 300 million starting in 2007.

Ironically Tamiflu is effective only when it's taken after the person has been infected and is beginning to feel symptoms of the disease.

Meanwhile, your best defense is minimizing your exposure to germs of all kinds and getting in the hand-washing habit.