In that great Hitchcock thriller, the birds start attacking Tipp Heron (Melanie Griffith's mom, for trivia fans) in Mendocino for no particular reason. Today, Ms. Heron works actively in films, international relief efforts and for animal causes. She may get an ironic opportunity to combine her charity works with birds again, because scientists around the world are looking nervously at the increasing possibility of a return of avian influenza, also known as the bird flu. First identified in Italy in 1900, it is the H5N1 virus implicated in the great Spanish Flu pandemic of 1918-1919 that killed about 40 million people. I say "implicated in" instead of "caused," because it was government policies that made the death toll much higher than it needed to be. But there is no doubt H5N1 is a major killer.

There are three steps H5N1 has to go through in order to get to people. First, there needs to be a lot of infected birds. Almost 200 million chickens have been killed or died in Asia in the last year due to avian flu infection. Strike One.

Next, unless someone eats diseased poultry, the flu has to cross species into an animal that can easily infect people. It has now crossed into pigs, which is where most human flu outbreaks begin. Pigs carry human influenza viruses. Viruses can combine (exchange DNA) in pigs, creating a variant of H5N1 that can spread as easily and rapidly as ordinary flu. Strike Two.

Finally, it has to hit an unprepared populace, with lowered immune systems and no effective drugs. Lowered immune systems are caused by, among other factors, cold weather, lack of sleep, excess weight, stress, high sugar intake and caffeine. Hmmm. Sound like anyone you know?

Serious scientists think H5N1 could kill as many people as the 1918 disaster, if only because there are now more than three times as many people in the world. The UN Coordinator for Avian and Human Influenza recently said a bird flu pandemic could kill as many as 150 million people. Other scientists have projected up to 354 million deaths. And you thought $3 gasoline was a major problem!

The H5N1 bird flu reappeared in Hong Kong in 1997. Eighteen people were infected, and six died. All the chickens in the area were slaughtered, and the outbreak was confined to Hong Kong. But it has now been found in Vietnam, Thailand, Japan, Mainland China, Malaysia and Indonesia.

It then showed up in Russia, almost certainly carried by migratory birds. So much for banning chicken. In August 2005, it appeared in Mongolia and Kazakhstan, and then in western Russia, poised to enter Europe. Romania found infected and dead swans in October. An infected parrot died in quarantine in the United Kingdom.

The Senior United Nations System Coordinator for Avian and Human Influenza in charge of a response to H5N1 says a pandemic could begin at anytime, and kill five million to 150 million people. He confirmed the virus is in migratory birds, and said an outbreak could start in Africa, where immune systems are chronically depressed, or the Middle East as well as Southeast Asia. What he didn't say is that the same migratory birds, mainly ducks, swans and geese, also travel thousands of miles to Canada and the U.S. The H5N1 virus is almost certainly in the U.S. already - it just hasn't been found yet. December, January and February are the "flu season" in both the U.S. and Asia.

We have reviewed all the companies involved in bird flu vaccines, and found two stocks that should be bought immediately because they will make a fortune even if there is never a case of bird flu in the world again. Governments around the world are stocking up on vaccines just in case they are needed, and these stockpiles need to be replenished periodically.