Gardasil, by Merck & Co. is successful at preventing warts and pre-cancerous lesions by 90 % in men, according to the largest study of the use of vaccine in males released Thursday by the vaccine's maker.

Anna Giuliano, a researcher at the H. Lee Moffitt Cancer Center in Tampa, Fla., who worked on the Merck study said, “We finally have something we may be able to offer men as well as women. It really opens the door to preventing infection and hopefully cancer and genital warts in males.'' Genital warts which are sexually transmitted are embarrassing and uncomfortable but is in no way life-threatening.

The results are said to give a boost to Merck’s sale of the drug, which declined 4 % in the third quarter, analysts said. Merck hopes to begin marketing it for boys soon, after asking the government for that approval later this year.

The new study involved about 4,000 males in nearly 20 countries ages 16 to 26. Results showed the vaccine was 90 % effective in preventing genital warts, with only 15 cases of persistent infection. This was compared to 101 cases in a group that was given a placebo vaccine. No serious side effects have been reported in the ongoing research and the results are after a 30 month study period.

Dr. Maura Gillison, an HPV researcher at Johns Hopkins University who was not involved in the Merck study said, "When parents are sitting in a room discussing with a pediatrician whether to vaccinate their child against anything, they'd like to know what the potential benefit is. A parent might say, 'I'm not inclined to vaccinate my child to prevent a benign genital wart."

Dr. Lauri Markowitz, an HPV expert at the U.S. Centers for Disease Control and Prevention said, "It's obviously encouraging data, but the policy makers will be looking at a variety of different issues," including how cost-effective the shot would be if used in males.

According to the Centers for Disease Control and Prevention HPV may cause about 1,500 men to develop penile cancer a year and 1,900 to get anal cancer. While 20 million Americans are infected with HPV, a majority will be able to fight off the infection naturally and about 1 % of sexually active men in the U.S. will develop genital warts from HPV. Gardasil is already approved for males in 40 countries worldwide.

The research, funded by Whitehouse Station, New Jersey-based Merck, is being presented today at the European Research Organization on Genital Infection and Neoplasia in Nice, France.