Federal health officials announced a human clinical trial of the first vaccine against West Nile infection, an injection that has been under study for the past six years and effectively prevented the disease in test animals.

Word of a possible vaccine comes as the ground and air war against mosquitoes and their larvae escalated in many parts of the greater metropolitan area.

Suffolk County had planned to conduct low-level spraying of adult mosquitoes with the pesticide Anvil Wednesday in the villages of Ocean Bay Park, Seaview and Ocean Beach on Fire Island. Last week, the New York City Department of Health used a helicopter to drop a larvicide in marshy areas of Queens and other nonresidential parts of the city.

The experimental vaccine was developed by scientists at the Oregon National Primate Research Center at the Oregon Health and Science University in Portland.

Investigators began working on the vaccine in 2009 when they were awarded a $7.2 million federal grant. The new vaccine is being tested in a Phase 1 clinical trial at Duke University, according to the National Institute of Allergy and Infectious Diseases, which is supporting the research.

Dr. Jorge Benach, director of Stony Brook School of Medicine's Center for Infectious Diseases, said he's encouraged that a vaccine trial is underway.

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"The burden of West Nile has become very important in the United States. I hope the vaccine is something that really works," Benach said.

West Nile virus, Benach added, is an animal pathogen harbored by birds and contracted by mosquitoes when they feed on fowl. People are infected when bitten by a female mosquito, which needs a blood meal to lay eggs. Mosquitoes are in flight from early spring through late fall.

Dickson Despommier, an emeritus professor of microbiology at Columbia University's Mailman School of Public Health and an expert in West Nile infection, said there were still too many unanswered questions about the vaccine.

"If they follow protocol, then the first run is for safety of the preparation. Just who should get the vaccine is another issue," Despommier said.

Federal health officials suggest -- but are not yet certain -- that the vaccine can be used in a diverse population, including people older than 65, one of the groups most vulnerable when infected by the virus.

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Scientists inactivated the virus to create the vaccine, which is called HydroVax-001. It is made with a novel, hydrogen peroxide-based process that kills the virus while maintaining key immune system triggering surface structures, federal health officials said.

In preclinical studies, the test vaccine protected mice against a lethal dose of West Nile virus.

The spread of the pathogen has become an annual rite of summer, experts said yesterday, following its sudden appearance in Queens in 1999.

"The most likely way West Nile virus arrived in this country was probably from airline passengers," Benach said. "Probably passengers arriving at Kennedy Airport. So I don't think it was coincidental that it first appeared in Queens."

Since the first case in Queens, the virus has increased exponentially in this country, Benach said.

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The National Institute of Allergy and Infectious Diseases estimates that last year there were 2,205 cases of West Nile disease and 97 deaths nationwide.