How Many HPV Vaccine Doses Are Enough?

In 2006, the FDA approved a vaccine against some types of human papillomavirus (HPV), which can cause cervical cancer. Gardasil® vaccinates against types 6 and 11, which cause 90 percent of genital warts, and types 16 and 18, which cause 70 percent of cervical cancers. It was originally approved for use in females ages nine to 26 and is now also approved for males of the same age. The FDA more recently approved Cervarix®, which vaccinates against types 16 and 18 and is only approved for females. Both vaccines are administered through three injections over six months; many individuals do not complete all three injections.  After the vaccines became available, cases of HPV dropped by 50 percent in the United States despite low vaccination rates.

Recent studies have suggested that receiving one or two doses of an HPV vaccine may be as effective as receiving all three injections recommended by the FDA. None of the studies show results more than four years following vaccination. Due to the high cost ($130/dose) and extended schedule to receive the vaccines, many individuals who begin the series do not complete it. Studies have shown that less than one third of individuals who receive one dose of the HPV vaccine complete the three-dose series.

HPV Infections

HPV are a group of more than 150 related viruses, more than 40 of which can be passed from one person to another through sexual contact occurring in the genitals, anal, or oral regions. Some types of HPV may cause benign (noncancerous) warts, or papillomas, but some types of HPVs, called “high-risk,” are associated with certain types of cancer. About 6 million new genital HPV infections occur each year in the United States, most of which occur without any symptoms and go away without any treatment over the course of a few years. Some HPV infections, however, persist for many years, with or without causing detectable cell abnormalities.

Infection with high-risk HPV is the major cause of cervical cancer. Almost all women will have an HPV infection at some point, though very few will develop cervical cancer. Only high-risk persistent HPV infections lead to cervical cancer. According to the National Cancer Institute, more than 12,000 women in the United States are diagnosed with cervical cancer annually, with more than 4,000 annual deaths occurring from cervical cancer. Worldwide, nearly half a million develop cervical cancer each year, with more than a quarter of a million casualties. Most anal cancers are also caused by high-risk HPV types. Anal cancer is less common than cervical cancer, but more than 5,000 men and women in the United States are diagnosed with the disease annually, with 770 deaths. High-risk HPV infection also causes some cancers of the mouth, throat, vulva, vagina, and penis.

HPV Vaccination

Gardasil® and Cervarix® (the HPV Vaccines) guard against viral infections to prevent future HPV infection. Neither provides complete protection against all HPV types; about 30 percent of cervical cancers overall will not be protected by the vaccines. HPV vaccination prevents nearly 100 of the precancerous cervical cell changes that would have been caused by HPV 16/18, and have been shown to provide protection against persistent cervical HPV 16/18 infections for up to eight years.

FDA-Approved Dosage

Both HPV Vaccines are designed to be given in three doses over a six-month period. The HPV Vaccines are proven to be effective only if given before HPV infection occurs; therefore, individuals should be vaccinated before they are sexually active. The three-injection series may be started for girls as young as nine; individuals who begin the series are recommended to complete all three doses regardless of age or duration between injections.

Fewer Dosages

In 2011, researchers found that four years after receiving the HPV vaccine, women who received only one or two injections were as well protected against HPV infection as those who received all three. In April, a study found that receiving two doses of HPV vaccine, rather than the recommended three, may be equally effective at protecting against HPV infection. Researchers determined that women who received two injections but did not complete the three-dose series had the same immune response to HPV infection as women who completed the full series, even three years after vaccination occurred.  It is unknown how well these women remain protected after more than three years, however.

The team that completed the 2011 study recently published a new study on the antibody stability in recipients of one, two, or three dosages of HPV Vaccine. It continues to suggest that one dose may effectively protect individuals against high-risk HPV infections linked to types 16 and 18, but  does not provide long-term results sufficient to change FDA recommendations. Researchers plan to continue studying the effects for 10-15 years.