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Microemulsion Shows Promise for Extending Vaccine Shelf Life

Maj. Jean Muderhwa (Courtesy, Jean Muderhwa)

Maj. Jean Muderhwa (Courtesy, Jean Muderhwa)

A U.S. Army medical researcher has devised a new process for mixing vaccine ingredients with the potential for extending the shelf life of vaccines. Maj. Jean Muderhwa (pictured left) , a deputy laboratory director at the Brooke Army Medical Center in San Antonio, presented his findings yesterday at a meeting of the American Society for Biochemistry and Molecular Biology.

Vaccine carriers are the substances that hold the active ingredients such as antigens in vaccines for delivery to the body. The need to stockpile vaccines, sometimes for years, however, calls for a way of preparing vaccines with carriers that make them suitable for long-term storage.

Muderhwa’s process uses a fine emulsion for suspending the active vaccine ingredients, with five common and stable components:

– Components 1 and 2 are oil and water, commonly found in many over-the-counter cream and lotion emulsions

– Component 3 is glycerol, also known as glycerine, another compound often found in common skin lotions

– Component 4 is a combination of acceptable surfactants in drugs, Span 80 and Tween 60; surfactants lower the surface tension between two liquids

– Component 5 is a protein with an aluminum-based adjuvant, an agent that enhances the response of an antigen

Emulsions make it possible to mix different kinds of ingredients in suspension, but the ingredients can separate over time, such as oil and vinegar in salad dressing. “If you make a vaccine containing an emulsion,” notes Muderhwa, “it’s only (good for) probably a few months because the emulsion is not thermodynamically stable. The surface tension is too high, and the molecules are repelling one another until the emulsion fails.”

To overcome this tendency for emulsions to separate, Muderhwa reduced the size of the suspended particles as much as possible. “The way you do that is you have to lower the surface tension to near zero,” says Muderhwa, using the surfactants Span 80 and Tween 60, and glycerol as a co-emulsifier to lower the surface tension of the tiny water and oil particles.

Microemulsions are used now for drug delivery in antibiotics and syrups, but they are also sensitive to change. To provide more stability to this carrier, Muderhwa added the same aluminum-based adjuvant approved for influenza vaccines.

This process’s physical properties have been studied in the lab, with animal tests planned for the near future. Muderhwa says research is also needed on the effect of the smaller surface area of antigens on immune response.

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