Liquid could aid vaccine storage, use. (Vaccine Design).

A new medium for vaccines could remove hurdles that impede immunization campaigns in poor countries. The innovation could eliminate, for most if not all vaccines, the need to either refrigerate or rehydrate doses before use, says Bruce J. Roser of the England-based firm Cambridge Biostability.

Most current vaccines spoil unless they're kept cold. That adds considerable expense and complexity to immunization campaigns in regions where electricity is scarce, says Bruce Weniger of the Centers for Disease Control and Prevention in Atlanta.

Some vaccines can instead be dehydrated for storage, but it takes trained health-care workers in the field to reconstitute them as liquids that can be administered.

To circumvent the need for either refrigeration or field preparation, Roser and his colleague Shevanti Sen turned to perfluorocarbons, which are chemically stable, nontoxic liquids.

To make vaccines without water, the researchers prepared microscopic spheres of sugar loaded with tetanus vaccine and suspended them in perfluorocarbons. Roser and Sen found that they could store this preparation for a month without sacrificing the vaccine's ability to stimulate an immune reaction in test animals. The micro-spheres fall apart inside the body and release the vaccine.

Researchers developing new vaccines, including those for AIDS, should move quickly to incorporate Roser's "refrigeration-free liquid" into their formulations, says Harriet L. Robinson of Emory University in Atlanta.

Applying the innovation to vaccines already on the market may be tricky, however, because new formulations require additional regulatory testing, says Weniger. With little financial incentive to cut through that red tape in wealthier countries, manufacturers are unlikely to change their vaccines for the sake of increasing sales in poor countries.

International agencies such as the World Health Organization could help create programs that guarantee a market for redesigned vaccines, Roser says. --B.H.