Dutch biotech Crucell NV said it will discontinue programs targeting West Nile virus, including its whole-killed West Nile virus vaccine and monoclonal antibodies, because the number of people infected has been decreasing over the past year.

Crucell, of Leiden, the Netherlands, informed investors of that move in its quarterly earnings report and pipeline update, stating that the commercialization opportunities for West Nile vaccines and treatments are "not as attractive as other products" in the company's pipeline.

To date, the firm has completed a Phase I trial for the whole-killed vaccine, demonstrating safety and tolerability, and was in the process of planning for Phase II when the program was halted.

That vaccine emerged from the company's PER.C6 technology, which uses an inactivated whole virus approach to grow the virus on PER.C6 cells before inactivating it for application in the vaccine.

Crucell also had been in preclinical development with a human monoclonal antibody that had demonstrated an ability to neutralize the West Nile virus in cell culture and fully protect against the virus in an animal model.

In 2003, when the firm began working on its West Nile vaccine, outbreaks of the virus were being reported all over the U.S. That year, the Centers for Disease Control and Prevention reported a total of 9,862 cases, including West Nile encephalitis, meningitis and fever, with 264 deaths.

In 2007, the CDC reported 3,576 cases and 115 deaths. Of the total cases, 65 percent were reported as West Nile fever, the milder form of the disease.

With the West Nile programs on the shelf, Crucell said it will continue focusing on its other development programs. In the vaccine space, the company has a Phase II-stage seasonal flu vaccine in partnership with Paris-based Sanofi Pasteur and expects to report results from Phase II studies of its H9N2pandemic flu vaccine in the first half of this year. Other vaccine programs are ongoing against Ebola, tuberculosis, malaria and HIV, and Crucell continues to advance antibody programs in rabies and H5N1 flu.

The firm, which reported a net loss of €4.8 million (US$7 million) for the fourth quarter, had cash totaling €163.2 million as of Dec. 31.

Shares of Crucell (NASDAQ:CRXL) lost 8 cents, to close at $13.42 Tuesday.