The H5N1 strain of avian influenza not only kills chickens quickly, but it can now infect people. The World Health Organization has confirmed 126 infections and 64 deaths, with another nine suspected or locally confirmed cases.

That doesn't sound like very many people.

It isn't -- yet. But H5N1 concerns health officials and scientists because, like all other flu strains, it is steadily changing. This virus lacks only the ability to pass among people the way ordinary, seasonal flu does.

If it acquires this transmissibility, it will infect millions of people within months and it may be more fatal, both because it is so pathogenic itself and because people do not possess any immunity to it.

When is this likely to happen?

No one can say. It might happen tomorrow, 10 years from now, or never. It is also possible the mutation process will cause this virus to lose its dangerous qualities.

So why not bet on the best outcome?

Because health experts agree that a big pandemic of something is overdue. In the last century there were three major pandemics of influenza -- the 1918 flu, which killed anywhere between 20 million and 100 million people, depending on the estimate, the 1957 flu, which killed about 4 million, and the 1968 flu, which killed about 1 million.

What can we do?

There is an experimental vaccine, but flu experts say it is unlikely to be a good match for the H5N1 strain that will eventually emerge. Using current technology it takes 6 months or more to make a new flu vaccine and there is no way to predict what the pandemic strain will look like, so no way to work ahead. Companies are trying to develop quicker and better ways to make flu vaccine but their efforts will take several years to bear fruit.

Will the regular flu vaccine help?

No. The seasonal flu vaccine provides no protection against H5N1. But health officials recommend getting it, not the least because regular influenza kills up to 500,000 people a year globally in a "normal" year.

What about drugs?

There are four drugs that work against influenza in general -- amantadine and rimantadine, Tamiflu, know generically as oseltamivir, and Relenza, known generically as zanamivir.

Tamiflu, invented by Gilead Sciences and made and sold by Swiss drug giant Roche AG, is the main choice. But its effects against H5N1 are not well known, it must be given early on in the infection to help, and it is in short supply.

Relenza, made by GlaxoSmithKline and invented by Australia's Biota Holdings, is considered equally effective but it is inhaled and might worsen asthma and related conditions.

H5N1 has shown some resistance to amantadine, meaning the virus has evolved mutations that make the drug less effective. It could also evolve resistance to Tamiflu and Relenza.

Countries are working to stockpile these drugs but current production is low and supplies are severely limited.

Surely modern medical practices will help?

In fact, public health around the world is in bad shape. Hospitals are filled to overflowing now and will not be able to cope with any serious epidemics. Many experts agree there is no reason to believe an influenza pandemic today will be less severe than in years past.

How can people protect themselves?

The same way they protect against any respiratory infection -- by regularly washing hands, or using an alcohol-based hand sanitizer, and by avoiding anyone who is obviously ill. Influenza viruses are carried in mucus, which people spread in droplets while talking, sneezing or coughing, or by touching their noses and mouths and then a surface.

If there is a pandemic, how bad it will be?