Half of men in the general population may be infected with human papillomavirus or HPV, the human wart virus that causes cervical and other cancers, strengthening the case for vaccinating boys against HPV, US researchers said on Monday.

US vaccine advisers have been weighing whether boys and young men should be vaccinated against the human papillomavirus, as they already recommend for girls and young women, but some worry the vaccine is too costly to justify its use.

HPV infection is best known as the primary cause of cervical cancer, the second most common cancer in women worldwide. But various strains of HPV also cause anal, penile, head and neck cancers. Vaccinating men and boys would prevent some of these cancers.

Anna Giuliano of the H Lee Moffitt Cancer Center and Research Institute in Tampa, Florida, and colleagues studied infection rates among more than 1,100 men aged 18 to 70 in the United States, Brazil and Mexico to get a snapshot of the natural progression of HPV infection in men.

“We found that there is a high proportion of men who have genital HPV infections. At enrollment, it was 50 percent,” said Giuliano, whose study appears online in the journal Lancet.

The team also found that the rate at which men acquire new HPV infections is very similar to women.

And they found that about 6 percent of men per year will get a new HPV 16 infection, the strain that is known for causing cervical cancer in women and other cancers in men.

Vaccines made by Merck & Co and GlaxoSmithKline both offer protection against this strain of HPV.

“The biology seems to be very similar (to women),” Giuliano said in a telephone interview.

“What is different is men seem to have high prevalence of genital HPV infections throughout their lifespans.”

She said it appears that women are better able to clear an HPV infection, especially as they age, but men do not appear to have this same ability.

Vaccine experts said the study builds momentum for widespread HPV vaccination among boys.

Currently, US Centers for Disease Control and Prevention recommends Gardasil vaccinations for girls and women between the ages of 11 and 26. Gardasil had sales of more than $1 billion last year.

And while doctors are free to use the vaccine in boys and men ages 9 through 26, US health officials so far have declined to recommend routine vaccination for males.

“This study highlights the high incidence of HPV infection in men, which emphasizes their role in transmission of HPV to women,” Dr. Anne Szarewski of the Wolfson Institute of Preventive Medicine in London said in a statement.

“It must surely strengthen the argument for vaccination of men, both for their own protection, and that of their partners.”

In December, the US Food and Drug Administration approved Merck’s Gardasil HPV vaccine for prevention of anal cancers in both men and women, based on studies showing Gardasil was effective in men who have sex with men, a group that has a higher incidence of anal cancer.

Anal cancer is one of the less common types of cancer, with an estimated 5,300 new US cases diagnosed each year, but the incidence is increasing.