A vaccine for the human papillomavirus (HPV) has a longer efficacy than originally thought.

Physicians at first believed the vaccine could only protect vaccinated patients for around five years. A study published in the journal "Pediatrics" on August 18 revealed the shot has been proven to protect against the sexually transmitted viruses for at least eight years.

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The study involved dividing 1,781 sexually inactive males and females between the ages of 9 and 15. Participants were divided into two groups: those given placebo shots and those injected with the HPV vaccine.

After eight years, those who received the shot still retained the antibodies that combat HPV.

HPV is believed to be the cause of the majority of cervical cancer cases.

Strains such as HPV 16 and 18 cause tumors. Transmission of the virus can result in genital warts in both men and women. Neck and head cancers can also be caused by HPV.

Head researcher Dr. Daron Ferris, director of the HPV epidemiology and prevention program at Georgia Regents University in Atlanta, said  "The body's response against HPV by making antibodies looks very good at eight years, and it seems like no booster doses will be necessary."

Ferris said the vaccine is so far proving to be safe, as well as effective in preventing diseases caused by the virus.

He encourages parents to get the child vaccinated, saying, "Thousands of people will continue to die each year if they are not vaccinated."

Despite the apparent efficacy of the vaccine, only around 57 percent of girls from the ages of 11 to 15 have been vaccinated and only 33 percent get the required three doses.

The U.S. Centers for Disease Control and Prevention (CDC) encourages children around the ages of 11 or 12 be given three shots of the HPV vaccine.

Ferris said the third injection is considered the booster dose that gives the patient long-term protection.