This year, there were two -- until Oct. 5, when one of them, Chiron Corp., announced that it would not be able to deliver 48 million doses bound for the U.S. market. The British government's drug-regulatory agency had impounded all doses made at Chiron's plant in Liverpool, England, because of bacterial contamination of some lots.
Now there is one left: Aventis Pasteur. Every flu shot that goes into an American arm this season will come from the French company's plant in the northeast Pennsylvania town of Swiftwater.
For two decades, Wyeth made injectable influenza vaccine at this plant in Marietta, Pa., which it eventually closed.
(Kalim A. Bhatti -- The Philadelphia Inquirer)
Wyeth has no second thoughts about being out of the market, even now, when the homely flu shot is the most sought-after medical commodity in the country.
"It was the right decision for us," Peter Paradiso, vice president for scientific affairs, said Friday. The company is concentrating on vaccines -- such as its ones for meningitis and pneumonia -- that have fewer competitors and don't need to be remade every year, he said.
The Centers for Disease Control and Prevention is scrambling to help reapportion what remains of Aventis's 55 million doses of flu vaccine -- about half the 100 million shots that were supposed to be on the market this fall. (There are about 2 million doses of FluMist as well, but it can be used only by healthy people ages 5 to 49.)
CDC director Julie L. Gerberding has repeatedly described the vaccine-production industry in the United States as "extremely fragile -- and getting more so." Flu vaccine isn't the only product that has had to be rationed in recent years. Several childhood vaccines have been in dangerously short supply, too. The current scarcity of flu shots reflects not only a larger problem but also forces unique to this vaccine.
Every year, hundreds of millions of people around the world contract influenza, and hundreds of thousands die. In the 1990s, the infection contributed to about 51,000 deaths each year in the United States, about 8,000 of them directly traceable to the virus, the CDC estimates.
Besides being contagious and deadly, flu virus mutates easily. Each winter gives the microbe a new opportunity to infect humans with slightly different versions of itself. These opportunities are augmented by the fact that three types of virus -- two influenza A strains and one B strain -- are circulating to one degree or another at all times.
The vaccine is made of a weakened strain of virus of each type. Generally, at least one strain each year undergoes so much mutation that it needs to be replaced by an "updated" version in the next year's vaccine. Consequently, a new flu vaccine formula has to be drawn up each year.
That's just one reason flu vaccine isn't very popular with vaccine makers. There are others.