Merck & Co.'s Gardasil vaccine, used to protect girls from getting cervical cancer, should not be given routinely to boys, a U.S. advisory panel said.

The immunization committee of the Centers for Disease Control and Prevention voted yesterday that Gardasil should be optional for boys rather than part of the approved childhood vaccination schedule. The shot is endorsed for routine use in girls 11 to 12 years old. It will be covered for boys and girls under a U.S. program for children who are uninsured or on Medicaid.

The Food and Drug Administration on Oct. 16 cleared the vaccine for males, ages 9 to 26, to prevent genital warts. Gardasil protects against a sexually transmitted infection called human papillomavirus, or HPV, that can lead to cervical cancer in women and to genital warts and cancer of the penis and anus in men. The benefits did not justify the cost of administering the vaccine to all boys, the panel said.

Decisions by the Advisory Committee on Immunization Practices are regularly adopted by the U.S. government.

A Merck spokeswoman, Pam Eisele, said in an e-mail that about "75 to 80 percent of males and females will acquire one or more types of HPV in their lives."

"As such, we believe there is value in vaccinating both young men and women with Gardasil."

The committee also voted yesterday to include GlaxoSmithKline P.L.C.'s competing vaccine, Cervarix, on the U.S. list of recommended vaccines for girls. Cervarix was approved Oct. 16 in the United States to prevent cervical cancer in females ages 10 to 25. Safety concerns contributed to a regulatory delay of Cervarix in 2007, giving Merck a huge head start.

The CDC's recommendation on Glaxo's Cervarix, once adopted, will tell doctors that both vaccines prevent cervical cancer, while Gardasil also protects against genital warts and cancer of the vagina and vulva. Language saying the panel had no preference for either vaccine was stricken after some members said wart protection made Gardasil a better shot.

Both shots are a three-dose series. The Merck series costs about $390, and Glaxo's costs about $385.