Wednesday, October 31, 2007

Adjuvants: Concerns temper the promise of the vaccine technology

In recent months, two major vaccine manufacturing power-houses (GSK and Sanofi-Pasteur) have announced results of clinical trials of pre-pandemic H5N1 vaccine using adjuvant, an antigen-sparing technology that may exponentially increase the manufacturing capacity of vaccine - particularly critical in a pandemic situation. In light of use of adjuvants, the WHO ramped up its forecast of available vaccine courses from a few hundred million to 4.5 billion (2 billion short of the projected global need, assuming mechanisms are in place to distribute the vaccine to everyone).

"(Adjuvants are chemicals that are incorporated in some vaccines to improve response to the vaccines' active ingredient. Adjuvants make it possible to reduce the dose of antigen in a vaccine without dampening the immune response.)"

Adjuvant presents obstacles though - some immunologic and others regulatory. The tradeoff of a possibly less safe vaccine may be acceptable in a pandemic - and regulatory hurdles (a particular problem in the US) are likely to be bypassed or sped up in a pandemic. Even so, concern remains.

"While adjuvants hold the greatest promise for dose-sparing, they also provoke trepidation because they are by definition immune-system activators. While many have been tested over the years, few have entered the market, because they proved too reactogenic to be acceptable to consumers or safe. Only one set of adjuvants, aluminum salts or alum (aluminum hydroxide, aluminum phosphate, and potassium aluminum sulfate), is licensed in the United States. Aluminum adjuvants and MF59, an oil-in-water emulsion that contains squalene (an oil found in some fish oils), are licensed in Europe."

"I have heard a lot of people say they expect problems with adjuvanted vaccines," said Hedwig Kresse, an associate analyst for infectious diseases with the British-based market analysts Datamonitor. "It is a technology that definitely has some potential, but there are a lot of issues that need to be addressed first".

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