An experimental vaccine designed to protect against the virus responsible for Cervical cancer performed well in a late-stage trial, drugmaker Merck & Co., said on Thursday.

The vaccines aim to protect against strains of the sexually transmitted Human papilloma virus (HPV), a cause of cervical cancer, the second-biggest killer of women worldwide.

Merck said a trial of 1,529 people found that younger adolescent males and females receiving the treatment called Gardasil experienced a higher immune response compared with young women.

The company said it was the first trial to look at young people ages 10 to 15 years old.

Merck is racing rival GlaxoSmithKline Plc, which is working on its own product called Cervarix, and analysts believe the drugmakers are headed for a fierce marketing battle.