DENVER - Human trials for the first West Nile virus vaccine should begin next spring, according to researchers working on the drug.

Scientists at Acambis Inc. of Cambridge, Mass., have been working on the vaccine since 1999, the first year West Nile turned up in the U.S. The first phase of human trials will probably start in March or April and involve 30 to 75 people. Those tests will likely happen in Kansas or Missouri.

In other trials, the vaccine has been used on monkeys, and they all developed immunity to the West Nile virus.

If the human tests are successful, and the vaccine is approved by the Food and Drug Administration, it could be on the market in about five years.

This year, the mosquito-borne germ has made around 3,580 people sick and killed 211.

About 380 horses in Colorado were infected after the virus was discovered in the state in August. The virus was also found in birds, including some at two zoos.

Twelve human cases have been confirmed in Colorado.
(The Associated Press contributed to this report. Copyright 2002 by 9NEWS KUSA-TV. All Rights Reserved)