Sanofi says H5N1 vaccine with adjuvant may go further

Editor's note: The title and first two paragraphs of this story were revised Dec 16 to correct a statement in the original that gave a more positive reflection of the trial results described below than may be warranted. The original version said that Sanofi Pasteur had described the trial results as "promising," but the company actually said only that the results were "a sign of progress."

Dec 15, 2005 (CIDRAP News) – Sanofi Pasteur today announced preliminary trial results suggesting that using an additive to boost the immune response may help to stretch the supply of a vaccine for H5N1 avian influenza by a modest amount.

Previous results had indicated that an H5N1 vaccine without an immune-boosting adjuvant would have to contain 12 times as much antigen (active ingredient) as seasonal flu vaccines do. In the results announced today, it took four times as much antigen as in a seasonal flu vaccine to induce an adequate immune response—an improvement, but far from what is needed to remedy the global shortage of vaccine production capacity.

Sanofi tested an H5N1 vaccine it is making for the French government on 300 volunteers, using three different doses: 7.5, 15, and 30 micrograms. The volunteers were divided into six groups, and each group received two doses of vaccine with or without alum, an adjuvant used in many vaccines, according to Len Lavenda, US spokesman for Sanofi. The shots were given 3 weeks apart.

"A 30-microgram dose with an adjuvant in a two-dose regimen demonstrated an immune response at levels consistent with requirements of regulatory agencies for licensure of seasonal influenza vaccine," the company said in a news release.

The two 30-microgram doses of vaccine containing alum induced an immune response in line with what the European Agency for Evaluation of Medicinal Products (EMEA) requires for flu vaccines, Lavenda told CIDRAP News.

"We saw responses in all six groups, but the two-30-microgram-dose adjuvant group was the only one within the range of EMEA approval," he said.

"The 7.5- and 15-microgram studies provided results that were not as high as the 30, but we are continuing to study that data and we expect to publish the full set within a few months," Lavenda said.

Seasonal flu vaccines typically contain 15 micrograms of antigen, the active ingredient, for each viral strain covered. The amount that proved adequate in the Sanofi trial was 60 micrograms (two 30-microgram doses), four times as much.

However, 60 micrograms is a much smaller amount than what was found to be adequate in a trial of an H5N1 vaccine that Sanofi is producing for the US government, according to results announced in August. In that trial, which didn't involve an adjuvant, the regimen that looked most promising was two 90-microgram doses, a total of 180 micrograms.

H5N1 vaccines are being developed in the hope that they will be protective if the H5N1 virus evolves into a pandemic strain. But even if the current experimental vaccines turn out be effective, the world's current production capacity is far too small to provide enough vaccine for more than a small fraction of the population, according to disease experts. Researchers hope that dose-sparing tools such as adjuvants will help stretch the supply.

Sanofi called the new trial results "a sign of progress" that will help guide further development of a pandemic flu vaccine. "Subsequent trials will explore different dosages, which may be helpful in answering questions about dose-sparing strategies," the company said.

The vaccine used in the latest trial is being developed to provide a stockpile for the French government, the company said. It comes from a different human isolate of H5N1 virus than the one used in the vaccine Sanofi is making for the United States, according to Lavenda.

See also:

Aug 8, 2005, CIDRAP News story "Hopeful news on human H5N1 vaccine, but production concerns considerable"

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