Manufacturing Problems With Swine Flu Vaccine : Shots - Health News Swine flu isolates aren't growing well in eggs, says WHO, and the manufacturing glitch could delay delivery of a vaccine by months.

Manufacturing Problems With Swine Flu Vaccine

Growing the new H1N1 virus in eggs is proving tough for vaccine makers / hide caption

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Even with the best-case scenarios, it was a very tall order -- make enough of a new swine flu vaccine to blunt the edge of a pandemic in time for flu season this fall.

Forget best-case. The World Health Organization says the virus that's being injected into eggs to create the pandemic vaccine is not growing well at all. Compared to seasonal flu viruses, it's growing only 25 to 50 percent as fast.

Scientists don't understand why. It seems a crucial surface protein on the new H1N1 virus, called hemagglutinin, is not very stable.

The bad news, announced at a press briefing today, has thrown vaccine researchers around the planet back to square one. They've scurried to isolate new samples of the virus from infected people and are working at top speed to hybridize those fresh strains with a standard flu virus that they know grows well in chicken eggs.

If they're lucky, they could have a new "seed strain" in hand later this month.

Not a moment to lose: Human tests with the pandemic vaccine are scheduled to begin in August. If those go well, manufacturers could still start cranking out the stuff by October.

(read past the jump to hear of hurdles that still loom)

"We hope the situation can be improved upon," says Dr. Marie-Paule Kieny, head of the WHO's Initiative for Vaccine Research. "But for the time being, there's no reason to be anxious."

Still, even if a higher-yield vaccine strain can be engineered, other hurdles loom. Nobody knows yet if the resulting vaccine will be as potent as seasonal flu vaccines. If not, it will require more viral protein per dose. So it will take vaccine manufacturers even longer to fill contracts with wealthy countries for an estimated 900 million doses of pandemic vaccine.

And in the worst case, after that, there wouldn't be any left for poorer countries at all.