While the researchers reported that levels of anti-HPV antibodies peaked seven months after the last shot, Harper noted they gave no information on how quickly those levels tailed off. In trials among girls and women, she said, some women lost immunity to vaccine strains within five years.
The bottom line, she said, is that the vaccine is effective in males against genital warts, a non-life-threatening condition that is one-tenth as common as abnormal Pap smears among women -- but has yet to be shown to be effective against more serious disease.
On the other hand, the study is well done, rigorous, and adds important information to the discussion of whether to strengthen the current permissive recommendation to vaccinate boys, commented Dr. William Schaffner of Vanderbilt University School of Medicine in Nashville, Tenn.
However, the data by themselves are not enough to "move the needle" toward a recommendation for universal vaccination, Schaffner said in an e-mail to ABC News/MedPage Today.
Like most experts reached by ABC News/MedPage Today, he said the cost of the vaccine is high and must be outweighed by its benefits -- an analysis that still needs to be done. "The higher the cost of the vaccine, the more benefit has to be demonstrated," Schaffner said.