Dr. Efren Domingo, president of the Society of Gynecologic Oncologists of the Philippines, said HPV subtypes 16 and 18 are responsible for 70 percent of cases of cervical cancer, the second most common cause of cancer death in women worldwide, as well as vulvar and vaginal cancers.
These two HPV subtypes are also responsible for "20 percent of head and neck cancers in men and women, anal and penile cancers, and as high as 70 percent of cancers in the anogenital region," he said.
The other 30 percent of cervical cancer cases are mainly caused by HPV subtypes 45, 52 and 55.
The vaccine, developed by Merck Sharp & Dohme (MSD), prevents not only those cancers caused by HPV subtypes 16 and 18, but also the pre-cancerous lesions and genital warts caused by these two HPV subtypes as well as HPV subtypes 6 and 11.
Domingo said MSD’s vaccine could also "cross-protect" against HPV subtypes 45, 52 and 55.
The virus, according to doctors, is transmitted mainly through sexual intercourse. However, Domingo said HPV may be transmitted "so long as there is intimate skin-to-skin contact."
"Some virgins have been shown to have HPV infection," MSD medical director Dr. Cesar Recto II said. "It can be a non-sexual act that may lead to infection, but this is very rare."
Domingo said HPV-related cancers in virgins involve the vulva and vagina, not the cervix. He added that even "non-penetrative" sexual acts such as oral sex and digital masturbation can spread the virus.
He also said that scientists are still studying whether the virus can be spread through skin contact with dirty toilets, objects and linens.
The Bureau of Food and Drugs (BFAD) approved the vaccine for use on males and females from nine years old up to 26 years old.
Since the ideal time to administer any vaccine is before exposure to infection, researchers studied the effects of the anti-cancer vaccine on children as young as nine.
"In other countries, the sexual debut – when a person experiences sexual intercourse for the first time – was found to be at 11 years old. In the Philippines, the age of sexual debut is 15 years old," Domingo said.
Domingo said he expects BFAD to approve the vaccine’s use on men and women 26 to 44 years by 2008 pending the results of an ongoing study involving subjects from this age group.
MSD’s vaccine is administered in three doses. The second dose is given one month after the first dose is administered, while the third dose is given six months after the first dose. Each dose, Recto said, is priced between P5,000 to P7,000.
Even if a woman is already infected with HPV, Domingo and Recto recommended that she still be vaccinated because "she may still be protected against other subtypes."
Being vaccinated against these HPV subtypes, however, does not make a woman exempt from routine Pap smears, which can detect changes in cervical cells before they progress to cancer.
Philippine Obstetrical and Gynecological Society president Dr. Susan Nagtalon said not all women who contract HPV will develop cervical cancer. A significant number will have the infection clear up in two years’ time, while a small number of women are at risk of progressing to cancer.