Where's my avian flu shot?

Health and medicine explained.
Oct. 20 2005 1:52 PM

Where's My Avian Flu Shot?

How to ramp up vaccine production.

Playing chicken with the flu
Click image to expand.
Playing chicken with the flu

If the bird flu that flew from Asia to Europe in mid-October mutates into a form that moves easily from human to human, historians will say of the 21st century's first pandemic: They knew what was coming. Public-health officials have known for four years that the avian virus—H5N1—is a nasty one that might jump to human-to-human transmission. Alas, forewarned doesn't mean forearmed. Clinical testing under way suggests we'll soon have a viable vaccine. But neither governments nor private vaccine-makers have a way to produce vaccines fast enough to prevent or contain an outbreak.

It's possible that bird flu may never jump to human-to-human transmission, or that it will jump but become less virulent, turning into the equivalent of an ordinary seasonal flu. But given that the virus has killed about half the 120 people known to have picked it up from birds, and that it bears disturbing genetic and clinical likenesses to the mass-killer Spanish flu virus of 1918, pumping up vaccine production makes sense. If there's a slim chance that tens or hundreds of millions of people will be killed, it's worth preparing for.

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In a pandemic scenario, a vaccine acts as both fire extinguisher and firewall. Having several hundred million doses of vaccine on hand globally, and the capacity to make more quickly, is the only realistic way to encircle and contain an initial local outbreak of bird flu—or, should containment fail, to keep infection and death rates from skyrocketing. This spring, health agencies around the world, including the U.S. National Institutes of Health, contracted with drug makers to develop and test bird-flu vaccines. The biggest trial under way so far, conducted by the NIH and the drug maker Sanofi-Pasteur, found that Sanofi-Pasteur's vaccine safely produces immunity in healthy adults. The NIH is now testing it on the elderly and children. Other drug makers, including Chiron, GlaxoSmithKline, and Medimmune, are running early trials of other formulations.

These efforts suggest that vaccine makers will be able to develop a seed supply of a reasonably effective vaccine within six months to a year. Producing mass quantities would take another six to nine months. (Click here for a Slate Explainer on how bird-flu vaccine is made.) In the best-case scenario, then, it will take at least a year—and more likely closer to two years—to produce a significant stockpile of vaccines, or 60 million to 90 million doses for the United States. (The goal shouldn't be to make billions of doses, because the virus might mutate radically before many of those shots could be given.)

What are our chances of pulling this off? A decade from now, they'll be quite good, as the planned expansion of industrial facilities and new, faster vaccine-development techniques ramp up production. But the shorter term is far dicier.

Currently, the drug industry can produce annually about 900 million doses of ordinary seasonal flu vaccine. But the bird-flu vaccines tested so far seem to require more raw antigen than do common flu vaccines (90 micrograms per doseinstead of 15). That means current methods can produce only about 150 million doses of bird-flu vaccine a year. Since effective vaccination requires two doses six weeks apart, those doses would vaccinate only 75 million people. That falls well short of the need.

Drug companiesmight be able to stretch the supply, however, by using an adjuvant—a chemical that magnifies a vaccine's effect. Several companies, including Sanofi-Pasteur, Chiron, GlaxoSmithKline, Medimmune, and Herispherx Biopharma, recently signed agreements with the United States and other countries to develop and test adjuvant-assisted vaccines. They hope to have these ready for approval by the Food and Drug Administration and the World Health Organization within a year or two. GlaxoSmithKline says its version will be powerful enough to stretch the current production capacity of 150 million shots of bird-flu vaccine to 7 billion shots—enough to vaccinate 3.5 billion people.

But a pandemic could still outpace the drug companies. That's one reason it also makes sense to prepare to cope in other ways—by coming up with a plan for maintaining essential infrastructure and services should a pandemic occur (we don't have one) and a way to quickly allocate, distribute, and administer antiviral drugs (we don't have that either). At the same time, the Bush administration and world health authorities need to keep pushing for and funding speedy vaccine development and manufacturing. Can the powers that be sustain that sort of interest? Their track record isn't encouraging. But the race is on.

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