Paula Murphy receives a shot of the experimental bird flu vaccine. She's one of the volunteers in a clinical study of the vaccine at the University of Maryland's School of Medicine in Baltimore.
Flu vaccines provide protection against the influenza virus by presenting the human body with something that looks like the flu virus but that does not cause disease. Our immune systems recognize this material and produce antibodies to it. If we are exposed to an actual flu virus, those antibodies will neutralize the virus and protect us.
Below, a look at the pros and cons of various vaccine production methods, either being used today or in development:
Pros: Millions of Americans receive this vaccine every year. It's safe and well tolerated. Its production begins in hens' eggs — a tried and true technology for 50 years.
Cons: The production method requires a great deal of planning. Eggs must be ordered many months in advance. Each dose of vaccine requires one egg, so millions of doses require millions of eggs. Also, it may be more difficult to make a bird flu vaccine using bird eggs.
Pros: This newer method of production results in a vaccine that has a flu virus that is crippled, so it can't cause disease. But the virus is not killed, as is the case in the standard vaccine. The vaccine also can be given as a nasal spray (FluMist is the brand name).
Cons: More expensive than standard vaccine, and also produced in eggs. Not approved for young children or older people.
Pros: This vaccine can be produced in giant vats of living cells (for flu, in dog kidney cells). Such a production method means it can be scaled up much faster than egg-based vaccines, making it more useful in a pandemic. Several versions have been tested successfully in people. One product is approved in the Netherlands.
Cons: Won't be widely available for a few years. The Food and Drug Administration is still assessing its safety. The dog cells, when injected in animals, can cause tumors. However, the vaccine itself does not contain any dog cells.
Pros: Instead of injecting flu virus proteins into people, this concept involves injecting just the DNA from a flu virus. Human cells then "read" this DNA and create proteins that act as a vaccine. Manufacture of DNA could be much faster than that of conventional vaccines.
Cons: The method is being tested in human clinical trials, but development could still take years, and it may not prove to be safe and effective.
Pros: Scientists would like to develop a flu vaccine that can be given just once and last for life, as is the case for some childhood vaccines. Current vaccines have to be tailored to protect against specific strains of flu viruses. This one, ideally, would protect against them all.
Cons: This is currently more a concept than an actual product, though scientists do have some strategies that could ultimately lead to a universal vaccine.
In December, Richard Harris reported about a push to develop new and faster methods of vaccine production. The current method, which requires the incubation of flu virus in hens' eggs, may not be up to the task of protecting people from a new strain of deadly flu. Listen to Harris' two-part report:
Image courtesy Chiron Corp.
Vaccine production at Chiron begins with hens' eggs, which are used to incubate the flu virus.
Image courtesy Chiron Corp.
Next week, a major vaccine manufacturer plans to start producing a shot that is designed to protect people against bird flu -- even though it's far from clear that a human vaccine developed now will be effective if the virus shifts into a more virulent form.
The disease has so far killed fewer than 80 people worldwide. But if the virus mutates and starts a global pandemic, it will take four to six months to design and start producing a vaccine based on that new virus. So the U.S. government is spending more than $160 million this year to build a small stockpile of vaccine based on the version of the flu virus that's killing birds today.
The vaccine against bird flu is being tested in humans at the University of Maryland Medical Center in Baltimore. The study is designed to see whether this shot is likely to work, and if so, at what dosage. Volunteers are paid $500-$600 to give blood, take shots and answer questions. Some receive the experimental vaccine; others get placebo shots filled with saltwater.
The government's plan to produce a human vaccine against H5N1, the bird flu that's swept through flocks in Asia, is a big gamble. The vaccine is based on a virus taken from a person in Vietnam who fell ill from bird flu. But it may not match the virus if it morphs into a form that could cause a pandemic. And this H5N1 virus may not end up causing a human pandemic at all. And if a vaccine is useful at all, there almost certainly won't be enough.
Researchers hope the vaccine will produce a protective immune response in study participants, says Dr. Anthony Fauci, head of the National Institute for Allergy and Infectious Diseases, which is funding the Baltimore study.
Unfortunately, it takes a large quantity of vaccine to stimulate that response: not just one shot but two. And each shot requires six times the dosage of the regular flu vaccine. That means companies will need to produce a massive amount of vaccine -- and they simply don't have the capacity to do so.
"It will take years to get stockpiles to the point you can effectively use it at the doses you want," Fauci says. But he says it's better to do what we can than to throw up our hands in despair. So the United States has asked two companies to start producing and stockpiling bird-flu vaccine.
One of the companies is Chiron, an American company with European plants and investors. It's one of two companies that supply most of the regular flu vaccine for the United States, and it is just recovering from recent manufacturing woes. In the fall of 2004, Chiron's Liverpool factory was shut down by health authorities, and that year's batch of vaccine was thrown away because of contamination.
But the plant has cleaned up its act and is back on line making regular flu vaccine. Moreover, the U.S. government has enough confidence in the Liverpool plant that it has paid Chiron $62 million to run off extra product: bird-flu vaccines for the government stockpile.
Chiron began manufacturing the experimental bird flu vaccine in early winter, during the brief break between the completion of this year's flu vaccine and the start of production of next year's vaccine. Production manager Philip Toms says the plant will run for just five or six weeks producing the bird flu vaccine. He won't say how much they'll make.
The process has taken considerable preparation. Chiron needs to be especially careful that the bird flu virus doesn't mix with human flu viruses. There's a remote chance that a new, deadly virus could emerge in that way.
The workers will also take extra precautions to make sure their own bodies don't become mixing vessels for these viruses. Workers will be required to don new protective suits that come with hoods designed to keep them from breathing in the virus.
An Unknown Shelf Life
But despite all these precautions in production, government scientists and public health officials around the world still have to deal with the fact that vaccines have a shelf life. And nobody knows how long the experimental bird flu vaccine will remain potent. If the vaccine doesn't last long, a stockpile could quickly turn into a compost pile.
Jim Robertson works at Britain's National Institute for Biological Standards and Control. This laboratory outside of London is responsible for designing flu vaccines for the World Health Organization and assuring their potency.
"Vaccines aren't wonderfully stable. You'll get 12 months out of it in the correct conditions, maybe 18 months, but it doesn't go on forever," says Jim Robertson of Britain's National Institute for Biological Standards and Control, which is responsible for designing flu vaccines for the World Health Organization and assuring their potency. "So again, it's a bit of a gamble to stockpile a few million doses. If it's not used, it's just going to go off."
People simply don't know how long flu vaccines last. They are tailor-made for each season, and whatever isn't used is thrown away. That's one reason some other nations are not planning to stockpile this bird flu vaccine. Robertson says the other big reason is that the next flu pandemic may have nothing whatsoever to do with the H5N1 bird flu. And even if it does, that virus could change so much between now and a pandemic that a vaccine against today's virus would be useless. The virus has already started to mutate, so it doesn't look exactly like the one that's being used in the vaccine.
Finally, there's the matter of vaccine supply. Chiron and other flu vaccine manufacturers can barely keep up with producing shots for the regular flu. There simply isn't capacity to produce huge amounts of bird flu vaccine for a stockpile. This year, the U.S. government hopes to acquire enough to treat 4 million people -- that's less than 2 percent of the U.S. population. Health officials are now looking at ways to stretch the supply, either by adding something to the shot to boost the immune response, or by changing the way the shots are given.
With all its uncertainties, this vaccine hardly sounds like a magic bullet. But health officials keep thinking back to 1918, when more than 50 million people died from flu. And they say, despite all the uncertainties surrounding a bird flu vaccine, anything that could help is worth pursuing.
Rebecca Davis produced this report.