In an assessment of the vaccine, whose success in early safety trials was unveiled last month, the British journal said the formula's low-dose approach meant it could be swiftly manufactured in an emergency.

The prototype is configured for the existing strain of H5N1 avian influenza, which is transmitted from poultry to humans.

If the virus ever mutated into a form that would make it easily transmissible from humans to humans, tens of millions of lives could be at risk.

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Present H5N1 vaccines are thought unlikely to have much effect against such a strain.

But the task of devising a specific vaccine against a pandemic strain becomes a lot easier if scientists can modify a basic H5N1 vaccine design which is already proven to be safe.

The Chinese vaccine was tested on 120 volunteers aged 18-60, who received two doses of a dummy lookalike formula or of the vaccine itself, at doses of 1.25 micrograms, 2.5, five and 10 micrograms, as well as an aluminum hydroxide booster to stimulate their immune systems.

After 56 days, researchers found that all of the vaccine doses produced antibodies against the virus, but the best response was in the 10-microgram group.

This dosage stimulated 78-percent protective antibodies, exceeding the European Union minimum requirement of 70 percent, and it was well tolerated with relatively few side effects.

The manufacturer is Beijing-based pharmaceutical firm Sinovac Biotech, which jointly developed the innoculation with China's Ministry of Science and Technology and its Center for Disease Control and Prevention.

In an online review of the work, British infectious-diseases specialist Iain Stephenson said the big advantage of the Chinese design was its successful use of a whole virus - rather than parts of it - to stimulate an immune response.

Whole-virus vaccines are known to trigger a bigger immune response than those made out of particles of the virus, although whole-virus designs are notorious for causing more side effects.

Therefore, if a whole-virus vaccine is safe, it can be used in lower dosages than partial-virus vaccines to get the same immune response - "a potential dose-sparing approach that could be crucial for a global supply of pandemic vaccine," Stephenson said.

Two previous vaccines have been tested for early safety and effectiveness: one provided protection at a dose of 90 micrograms, and the other at a dose of 30 micrograms.

Limits on present manufacturing capacity means that, within the crucial first six months after the start of a pandemic, vaccine plants could only churn out enough doses to protect 75 million or 225 million people, respectively, Stephenson said.

But a low-dose vaccine of 10 micrograms would mean sufficient doses for 450 million people could be produced during this time, he calculated. AGENCE FRANCE-PRESSE