Chiron Corp.'s stock dropped 18 percent on Monday on the news thatits prophylactic genital herpes vaccine had failed in Phase III trials.

Chiron said it will not pursue a product license application for thevaccine based on results from the trials, which did not indicateefficacy for the product.

Specific results of the trials, Kimberly Sankaran, manager ofcorporate communications told BioWorld Today, "were notstatistically significant," however, the company had decided to waitto report specific results at an appropriate scientific forum.

"People were shocked," Reijer Lenstra, an analyst with Smith BarneyShearson in New York said. "This vaccine is the most importantproduct in Chiron's pipeline, the cornerstone of its new vaccinebusiness, and the first of its new vaccines," Lenstra said.

"The fact that it didn't work has shaken confidence," he added,"although , I think it will be very difficult to make vaccines for thesetypes of chronic infections."

Chiron, however, reported last January that the Phase III study failedto meet its primary endpoint. (See BioWorld Today, Sept. 19, 1996,p. 1.)

Two Phase III trials were conducted, Sankaran said. The first focusedon 500 herpes simplex virus type II (HSV-2) uninfected volunteers,who were from discordant couples in which one was infected and theother was not.

The second trial studied 2,000 uninfected volunteers who wererecruited from clinics at which individuals with sexually transmitteddiseases were treated. In each case, the volunteers were immunizedwith three doses at zero, one and six months with either the vaccineor an adjuvant. The patients were followed for one year after finalimmunization at the end of which they were tested for HSV-2infections.

Phase II results of the vaccine, reported the company, indicated it tobe highly immunogenic and well tolerated. Persons negative forHSV-2, who received 30 mg immunizations each of recombinantglycoprotein gD2 and gB2 in the MF59 adjuvant, developedantibodies to the major neutralizing glycoproteins of HSV-2 thatwere 100 times greater than that achieved by previous glycoproteinpreparations tested in the same assay.

Eighty-eight percent of the HSV-1 seropositive patients and 72percent of HSV-seronegative patients developed neutralizingantibody responses to HSV-2 that equaled or exceeded those in anunselected cohort of persons with naturally acquired HSV-2infection.

The epidemiologic studies showing that HSV-2-specific immuneresponses appeared to protect against reinfection, transmission toneonate and transmission between sexual partners all supportoptimism about the potential utility of the vaccine.

Chiron, located in Emeryville, Calif., has total revenues of $1.1billion for the year ended Dec. 31, 1995.

Chiron's stock (NASDAQ:CHIR) closed Monday at $18.125, down$3.750. n

-- Frances Bishopp

(c) 1997 American Health Consultants. All rights reserved.