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Scientists have used a new method to make stockpiles of bird flu vaccine go further, saying more people could be vaccinated in the event of a pandemic.

Geert Leroux-Roels, from the Belgium-based Centre for Vaccinology at Ghent University, and colleagues published their results in the Lancet last week (17 August).

They combined a vaccine, derived from a sample of H5N1 virus collected in Vietnam in 2004, with an adjuvant — a chemical that boosts a person's immune response to a vaccine.

Adjuvants are added to vaccines to reduce the amount of vaccine needed to induce a protective immune response, and so that more doses can be made from the vaccine stockpile.

Four hundred healthy volunteers between the ages of 18–60 were given two doses of vaccine, 21 days apart. Half the volunteers received the adjuvanted vaccine and the other half the control vaccine.

The researchers found that even at a low dosage, the adjuvanted vaccine induced a protective immune response, while the control vaccine at the same dosage did not.

Reducing the amount of vaccine in one dose is important because most people — having never been exposed to the bird flu H5 protein — will need two doses, says Lerouz-Roels, and stockpiles will need to go further.

The researchers also found that 77 per cent of the people vaccinated with the lowest dose of adjuvanted vaccine also possessed antibodies capable of combating a second H5N1 virus, sampled in Indonesia in 2005.

Leroux-Roels told SciDev.Net that the vaccine's ability to respond to another type of H5N1 means it is a good candidate to use before a pandemic has started and before the exact type of H5N1 causing it is known.

John Oxford, a professor of virology at the UK-based Queen Mary School of Medicine, said the ability of this vaccine to protect across several strains is extremely positive.

"As little as a year ago, people imagined vaccines would have to be very specific," he told SciDev.Net.

He noted that vaccine research isn't being hampered by Indonesia's past refusal to share H5N1 samples from bird flu patients for vaccine research with the World Health Organization.

Indonesia has not sent a usable sample this year, according to the Reuters news agency. The country is concerned poor countries will not be able to afford or be given access to vaccines derived from the samples.

But Oxford says, "There are enough samples for vaccine researchers and by providing samples, South East Asian countries are doing a very positive thing for which they will receive vaccine in return."

Link to summary of the paper in the Lancet*

Reference: The Lancet 370, 580 (2007)

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