VOA常速英语:Combined Smallpox-Anthrax Vaccine Passes Early Tests

Researchers have developed an improved version of the smallpox vaccine that can be combined with a vaccine against anthrax. The dual vaccine represents a significant scientific achievement as well as a possible improved defense against biological attack.

The World Health Organization declared smallpox eradicated in 1980.

Few people under age 40 have been immunized against the disease, so officials in the U.S. and elsewhere are concerned that smallpox might be used as a biological weapon.

The existing vaccine is essentially an improved version of the smallpox vaccine developed by Edward Jenner more than two centuries ago. It uses a live virus - not smallpox, but a related bug called vaccinia - which prompts the body to mount an immune response that  protects against smallpox, too.

Unfortunately, the vaccine can sicken some people, especially those with weakened immune systems, including organ transplant patients and people infected with HIV.

Researchers led by Liyange Perera of the U.S. National Cancer Institute have developed a modified vaccine by adding a gene to the vaccinia virus.

"We were hoping that by sticking this gene into the existing virus, we can reduce the residual virulence of this vaccine because the immune system would see this vaccine more efficiently and clear the viral infection," Perera said. "So that indeed was the case with the actual experiment."

The researchers found that the modified vaccine was not only safer, but also more effective in prompting an immune response in laboratory animals.

"Not only [have we] eliminated the residual virulence of the old smallpox vaccine, but at the same time we have increased the robustness of this vaccine as well," Perera said in a telephone interview from Tokyo.

But there's more: the Sri Lankan researcher and his team added another gene that, in effect, makes anthrax vaccine. The combination appears to be faster-acting than the existing anthrax vaccine.

Further tests of the new vaccine are planned. In any event, it will probably be at least several years before it is ready for distribution.

Liyange Perera and his colleagues describe their new vaccine and how they made it in the Proceedings of the National Academy of Sciences.