(Reuters) - GlaxoSmithKline's herpes vaccine failed to protect women against the virus in a trial, the U.S. National Institutes of Health said Thursday, and the company said it was stopping development of the product.

The test of 8,000 women in the U.S. and Canada showed the Simplirix vaccine failed to protect them significantly from the virus, which causes genital herpes, the National Institute of Allergy and Infectious Diseases said in a statement.

"The estimate of vaccine effectiveness was 20 percent, but all estimates have statistical uncertainty, and this effect was not substantially different from zero," the NIH said.

The Phase III trial, the last step before regulatory approval of a drug or vaccine, was sponsored by Glaxo at 50 sites in the U.S. and Canada.

The women, aged18 to 30, all started out free of infection by either the herpes simplex 1 virus that causes cold sores or the related HSV-2, which causes genital herpes.

Half got the herpes vaccine along with an immune system booster called an adjuvant, and half got Glaxo's hepatitis A vaccine instead.

"GlaxoSmithKline has made the decision not to pursue further worldwide development of Simplirix," the company said in a statement, saying it made the decision after getting the results of the trial.