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Radiation may offer better way to make vaccines

“Vaccines often protect mice but not people so the idea must be tested more,”....

WASHINGTON (Reuters) - Vaccines made with bacteria killed by gamma rays may be more effective than those made using standard heat or chemical inactivation, U.S. government researchers said on Wednesday.

Such vaccines do not have to be kept cold, the team at the University of California, San Diego, School of Medicine reported in the journal Immunity.

Dr. Sandip Datta and colleagues made a vaccine from Listeria monocytogenes bacteria, a common cause of food poisoning.

The Listeria were killed with gamma rays and the vaccine protected mice infected with live Listeria, unlike vaccines made with heat-killed bacteria.

"This advance is potentially of great importance in meeting the challenge of creating vaccines that are safe, effective and simple to manufacture and transport," said Dr. Elias Zerhouni, head of the National Institutes of Health, which paid for the study.

"Although completely inactivated by the radiation, and thus unable to cause illness, irradiated bacterial pathogens evidently retain characteristics that prompt the immune system to mount a full-fledged defense," Datta said in a statement.

Vaccines can be made in three ways -- using an attenuated, or weakened, form of live bacteria or virus, using a killed germ, or using pieces of DNA from a bacteria or virus.

Most attenuated vaccines must be kept cold, but the UCSD researchers found that mice could be protected by vaccination with irradiated Listeria that had been freeze-dried into a powder.

This might mean that such vaccines could be used in hot places without electricity, the researchers said.

Vaccines often protect mice but not people so the idea must be tested more, the researchers noted.