Every influenza strain requires a different vaccine. Typical flu shots include two, three or more strains of <und>current</und> human influenza viruses that public health officials guess might be the most likely to be spread around.

Vaccines are wonderful, but slow. It takes several months to develop a vaccine using current methods (which utilize - tada - CHICKEN EGGS), and several more months to manufacture large quantities and distribute them worldwide. Some new techniques may speed up the development process but the manufacture and especially distribution will still be slow.

The 1918 flu spread around the world in 6 months, with 1/3 the current world population and much slower means of tranportation. And development of a specific vaccine against a human pandemic strain might not be able to be started until after the first outbreak occurs and the exact virus identified.

Antiviral medications may offer more hope as they could be manufactured and distributed in advance, but the costs would be huge. Guess which countries will get the biggest share, soonest. Who really cares about the Third World, anyway?

"It takes a little over a month for us to develop a recombinant vector vaccine compared to a minimum of several months via traditional methods," he explained. "This capacity will be particularly invaluable if the virus begins to mutate rapidly, a phenomenon that often limits the ability of traditional vaccines to contain outbreaks of mutant strains." Dr. Gambotto added that his group is planning a small clinical trial of the vaccine in humans in the very near future.

Science Daily

With today's long vaccine production timelines, it's not possible to develop new vaccines against newly formed flu viruses as rapidly as desired. Can this be corrected?
Yes. The problem with all of the vaccines mentioned above is that they use 50-plus year-old technology in which the vaccine is produced using chicken eggs. This process is slow. If a highly contagious bird flu strain were identified today, it would take a minimum of four to six months to make and distribute the first doses of a vaccine against it.

New technologies, however, are on the horizon. Primary among those technologies is one that uses mammal cells instead of eggs. Scientists would grow and store mammal cells, such as dog (canine) kidney cells, in large quantities so that they'd be ready and waiting. As soon as a flu strain becomes apparent, scientists could inject those mammal cells with the virus. The cells would burst and die and scientists could quickly harvest the resulting influenza proteins and distribute them to humans as a vaccine.

Mayo Clinic

Influenza pandemic timeline:

March 11, 1918 - first documanted case of what would be called "Spanish Flu" occurs at Fort Riley, Kansas.
October, 1918 - crime rate in Chicago drops by 43% due to sick crooks
- 195,000 Americans die of "Spanish" influenza
Nov. 21, 1918 - sirens sound in San Francisco announcing that it is safe for everyone to remove their face masks.
Dec. 1918 - 5,000 new cases of influenza are reported in San Francisco.
End of 1919 - The Bulletin of the History of Medicine reports that the estimate of the numbers dead from the 1918 epidemic has again been revised. The newest estimate is that between 50 million and 100 million died. Includes 675,000 Americans. The death rate for 15 to 34-year-olds of influenza and pneumonia were 20 times higher in 1918 than in previous years (that's rate, not total - the totals were vastly greater)
Feb. 6, 2004 - Researchers working separately at the Scripps Institute in La Jolla, California and at Britain's Medical Research Council discover that the 1918 virus may have jumped directly from birds to humans rather than going from birds to pigs and then infecting humans. They say it explains why the 1918 strain was so deadly, since human immune systems aren't prepared for viruses coming directly from birds.

Various influenza pandemics:
1918-1919
39 years later:
1957 - 100,000 die worldwide.
11 years later:
1968 - 700,000 die.
It has now been 38 years since 1968.

As of today, H5N1 has been found in birds in the following countries (aproximate chronological order): China, Vietnam, Thailand, Indonesia, Malaysia, Cambodia, Philippines, Khazakstan, Turkey, Romania, Bulgaria, Russia, Croatia, Kuwait, Iraq, Azerbaijan, Greece, Italy, Bulgaria, Iran, Austria, Germany

(Various sources)