Inoculating an egg with a sample of the H5N1 avian influenza virus

Greg Knobloch, CDC

[Beijing] Two studies, one Chinese and one US, show potential for producing flu vaccines to protect people against a bird flu pandemic.

The US study, published in PLoS Medicine today (12 September), suggests it could be possible to produce a vaccine that would protect against future strains of H5N1.

The Chinese team's vaccine, meanwhile, is more effective at protecting against infection than any other so far.

Led by Kanta Subbarao of the US National Institute of Allergy and Infectious Diseases, the US team produced three vaccines by combining a common flu virus with key proteins from H5N1 viruses collected in 1997, 2003 and 2004.

Mice that were given a single dose of the vaccines did not die when they were later infected with H5N1 — the unprotected mice, however, did.

Moreover, the researchers found that mice and ferrets that were given two doses of the vaccines were protected against a later strain of H5N1 — one that had been collected in 2005.

So far, researchers and policymakers have been concerned that production of a vaccine against a pandemic form of H5N1 would only begin once the pandemic virus had emerged — and therefore after the pandemic itself had begun.

The Chinese vaccine, produced by Sinovac Biotech, contained an inactivated version of the whole H5N1 virus and adjuvant — a chemical that is sometimes added to vaccines to make it more effective.

In a previous trial of an H5N1 vaccine developed by Sanofi Pasteur, researchers found that they needed 30 micrograms of virus for their vaccine to adequately protect humans against bird flu.

But results published online in The Lancet last week (7 September) show that the Sinovac Biotech vaccine achieved its best response with only two doses of ten micrograms of virus when it was tested in 120 people.

Minimising the amount of virus needed in a vaccine to protect humans is important because of the time it takes to grow the virus, making it more difficult to produce enough vaccine to meet global demand.

Vaccines made of whole viruses, such as the Chinese vaccine, are known to trigger greater immune responses than those made out of virus particles, such as the US vaccine. However, they are thought to be more risky.

But Yin Weidong, president of Sinovac, told SciDev.Net: "The lower safety of the whole-virus vaccines is a conclusion resulting from biotechnological levels of more than one decade ago. The newest technologies can make the whole-virus vaccine better purified and reduce the possibility of side effects."

Link to full paper by Subbarao et al in PLoS Medicine

Link to abstract of paper by Yin et al in The Lancet*
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References:
PLoS Medicine 3(9): e360 (2006)
The Lancet 367:1657-1664 (2006)