West Nile: Beware the Bug's Bite 

Acambis, a U.K.-based company, developed the vaccine based on its yellow fever vaccine, which doctors have used successfully for about 70 years. Yellow fever is a flavivirus, the same class of virus as West Nile. To create the new vaccine, researchers replaced key yellow fever genes with West Nile genes.

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"The original yellow fever vaccine has been in approximately 300 million people worldwide and is considered one of the safest vaccines available," Alan Lamont, director of business development for Acambis, wrote in an e-mail.

Studies have shown the West Nile vaccine to be safe and effective in laboratory animals, including monkeys, the NIH said Tuesday at a press briefing held by the Centers for Disease Control and Prevention.

"It looks like our best bet," said Dr. Jim Meegan, program officer for viral diseases at the National Institute of Allergy and Infectious Diseases, a division of the NIH.

Acambis is one of several companies in the running to develop a vaccine for West Nile. Its competition includes AVI BioPharma of Portland, Oregon, and Vical, based in San Diego.

The Vaccine Research Center of the NIH has asked Vical to manufacture a high-quality batch of doses that can be tested in humans.

Vical specializes in what are called "naked DNA vaccines." Whereas conventional vaccines use the largest amount of a pathogen possible to prevent a disease without making a person sick, naked DNA vaccines use the smallest amount of the pathogen possible.

Vical's vaccine is created using two West Nile proteins that don't cause the illness but induce an immune response to the disease.

"We encode the recipe for the pathogen," said Vijay Samant, CEO of Vical.

The company is currently working on vaccines for HIV, anthrax, Ebola and several other diseases in addition to West Nile.

"What we do with this technology is cut out the gene carried by the pathogen in a cassette-type plug-and-play system and pop it into a circle (called plasmid rings) of DNA," said Dr. David C. Kaslow, chief scientific officer at Vical. "We quickly grow it up in bacteria, and we're ready to go into safety studies."

But the Food and Drug Administration has not yet approved any naked DNA vaccines for use in humans. And some test results suggest that people who get the vaccines may require booster shots because it is difficult to get naked DNA vaccines to replicate enough in patients' bodies to induce immune responses.

That said, a vaccine for West Nile can't come too soon to stave off the disease, officials say.

The CDC expects West Nile to spread throughout the United States this year. Last year it infected people in 44 states.

The first cases of the summer already have turned up in South Carolina and Texas, and they showed up nearly a month earlier than last year's first cases.

West Nile, which is spread by mosquitoes, is a potentially serious illness, but about 80 percent of those who have the disease don't even know they are infected.

Twenty percent of those infected have fevers, headaches, body aches, nausea and sometimes swollen lymph glands or a skin rash for a few days. About one in 150 develops more severe symptoms, including stupor, coma, vision loss and paralysis.

Dr. Julie Gerberding, director of the CDC, said the most immediate solution to West Nile is to avoid infection by using bug spray and wearing long sleeves.

"For right now, the most important thing people need to do is be prepared and take the steps necessary to prevent mosquito bites," she said.