Published by the National Cancer Institute (NCI)
What are human papillomaviruses? Human papillomaviruses (HPVs) are a group of more than 100 related viruses. They are called papillomaviruses because certain types may cause warts, or papillomas, which are benign (noncancerous) tumors. The HPVs that cause the common warts that grow on hands and feet are different from those that cause growths in the throat or genital area. Some types of HPV are associated with certain types of cancer. These are called “high-risk,” oncogenic, or carcinogenic HPVs.
Of the more than 100 types of HPV, over 30 types can be passed from one person to another through sexual contact. Transmission can occur in the genitals, anal, or mouth regions. Although HPVs are usually transmitted sexually, doctors cannot say for certain when infection occurred. About 6 million new genital HPV infections occur each year in the United States. Most HPV infections occur without any symptoms and go away without any treatment over the course of a few years. However, HPV infections sometimes persist for many years, with or without causing detectable cell abnormalities.
Do HPV infections cause cancer? Infection with certain types of HPV is the major cause of cervical cancer. Almost all women will have an HPV infection at some point, but very few will develop cervical cancer. The immune system of most women will usually suppress or eliminate HPVs. Only HPV infections that are persistent (do not go away over many years) can lead to cervical cancer. In 2009, more than 11,000 women in the United States will be diagnosed with this type of cancer and about 4,000 will die from it. Cervical cancer strikes nearly half a million women each year worldwide, claiming more than a quarter of a million lives. Studies have found that HPV infection is also a strong risk factor for oropharyngeal cancer (cancer that forms in tissues of the oropharynx, which is the middle part of the throat and includes the soft palate, the base of the tongue, and the tonsils) (1, 2). Studies also suggest that HPVs may play a role in cancers of the anus, vulva, vagina, and penis.
Can HPV infection be prevented? The surest way to eliminate risk for genital HPV infection is to refrain from any genital contact with another individual.
For those who choose to be sexually active, a long-term, mutually monogamous relationship with an uninfected partner is the strategy most likely to prevent genital HPV infection. However, it is difficult to determine whether a partner who has been sexually active in the past is currently infected.
It is not known how much protection condoms provide against HPV infection, because areas not covered by a condom can be infected by the virus. Although the effect of condoms in preventing HPV infection is unknown, condom use has been associated with a lower rate of cervical cancer, an HPV-associated disease.
The U.S. Food and Drug Administration (FDA) has approved two vaccines to prevent HPV infection: Gardasil® and Cervarix®. Both vaccines are highly effective in preventing persistent infections with HPV types 16 and 18, two high-risk HPVs that cause most (70 percent) cervical cancers. Gardasil also prevents infection with HPV types 6 and 11, which cause virtually all (90 percent) genital warts (3). In addition, there is some initial evidence that Cervarix provides partial protection against a few other HPV types that can cause cancer, but further evaluation is required before the magnitude and impact of this effect is understood.
What are Gardasil and Cervarix? The Gardasil vaccine, which is produced by Merck & Co., Inc. (Merck), is called a quadrivalent vaccine because it protects against four HPV types: 6, 11, 16, and 18. Gardasil is given through a series of three injections into muscle tissue over a 6-month period. The FDA has approved Gardasil for use in females for the prevention of cervical cancer, and some vulvar and vaginal cancers, caused by HPV types 16 and 18 and for use in males and females for the prevention of genital warts caused by HPV types 6 and 11. The vaccine is approved for these uses in females and males ages 9 to 26.
Cervarix is produced by GlaxoSmithKline (GSK). It is called a bivalent vaccine because it targets two HPV types: 16 and 18. This vaccine is also given in three doses over a 6-month period. The FDA has approved Cervarix for use in females ages 10 to 25 for the prevention of cervical cancer caused by HPV types 16 and 18.
Both Gardasil and Cervarix are based on technology developed in part by National Cancer Institute (NCI) scientists. NCI, a component of the National Institutes of Health, licensed the technology to two pharmaceutical companies—Merck and GSK—to develop HPV vaccines for widespread distribution.
Neither of these HPV vaccines has been proven to provide complete protection against persistent infection with other HPV types, although some initial results suggest that both vaccines might provide partial protection against a few additional HPV types that can cause cervical cancer. Overall, therefore, about 30 percent of cervical cancers will not be prevented by these vaccines. Also, in the case of Gardasil, 10 percent of genital warts will not be prevented by the vaccine. Neither vaccine prevents other sexually transmitted diseases, and they do not treat HPV infection or cervical cancer.
Because the vaccines do not protect against all HPV infections that cause cervical cancer, it is important for vaccinated women to continue to undergo cervical cancer screening as recommended for women who have not been vaccinated.
How do HPV vaccines work? The HPV vaccines work like other immunizations that guard against viral infection. The investigators hypothesized that the unique surface components of HPV might create an antibody response that is capable of protecting the body against infection and that these components could be used to form the basis of a vaccine. These surface components can interact with one another to form virus-like particles (VLP) that are noninfectious and stimulate the immune system to produce antibodies that can prevent the complete papillomavirus from infecting cells. They are thought to protect primarily by causing the production of antibodies that prevent infection and, consequently, the development of cervical cell changes (as seen on Pap tests) that may lead to cancer (4). Although these vaccines can help prevent HPV infection, they do not help eliminate existing HPV infections.
How effective are the HPV vaccines? Gardasil and Cervarix are highly effective in preventing infection with the types of HPV they target. Studies have shown that both Gardasil and Cervarix prevent nearly 100 percent of the precancerous cervical cell changes caused by the types of HPV targeted by the vaccine for up to 4 years after vaccination among women who were not infected at the time of vaccination (5, 6, 7).
Why are these vaccines important? Widespread vaccination has the potential to reduce cervical cancer deaths around the world by as much as two-thirds, if all women were to get the vaccine and if protection turns out to be long-term. In addition, the vaccines can reduce the need for medical care, biopsies, and invasive procedures associated with follow-up from abnormal Pap tests, thus helping to reduce health care costs and anxieties related to abnormal Pap tests and follow-up procedures (4).
How safe are the HPV vaccines? Before any vaccine is licensed, the FDA must determine that it is both safe and effective. Both Gardasil and Cervarix have been tested in tens of thousands of people in the United States and many other countries. Thus far, no serious side effects have been shown to be caused by the vaccines. The most common problems have been brief soreness and other local symptoms at the injection site. These problems are similar to ones commonly experienced with other vaccines. The vaccines have not been sufficiently tested during pregnancy and, therefore, should not be used by pregnant women.
A recent safety review by the FDA and the Centers for Disease Control and Prevention (CDC) considered adverse side effects related to Gardasil immunization that have been reported to the Vaccine Adverse Events Reporting System since the vaccine was licensed (8). The rates of adverse side effects in the safety review were consistent with what was seen in safety studies carried out before the vaccine was approved and were similar to those seen with other vaccines. However, a higher proportion of syncope (fainting) and venous thrombolic events (blood clots) were seen with Gardasil than are usually seen with other vaccines. Falls after syncope may sometimes cause serious injuries, such as head injuries. These can largely be prevented by keeping the vaccinated person seated for up to 15 minutes after vaccination. The FDA and CDC have reminded health care providers that, to prevent falls and injuries, all vaccine recipients should remain seated or lying down and be closely observed for 15 minutes after vaccination. More information is available on the CDC’s Web site at http://www.cdc.gov/vaccinesafety/Vaccines/HPV/Index.html on the Internet.
How long do the vaccines protect against infection? The duration of immunity is not yet known. Research is being conducted to find out how long protection will last. Phase III clinical trials have shown that Gardasil and Cervarix can provide protection against HPV16 for 4 years. Smaller studies have suggested that protection is likely to last for longer than 4 years, but it is not known if protection conferred through vaccination will be lifelong.
Note from SaneVax: See the following quote from above, it confirms that HPV vaccination is a huge public health experiment at the expense of our children and the public health care budget.
Gardasil and Cervarix are highly effective in preventing infection with the types of HPV they target. Studies have shown that both Gardasil and Cervarix prevent nearly 100 percent of the precancerous cervical cell changes caused by the types of HPV targeted by the vaccine for up to 4 years after vaccination among women who were not infected at the time of vaccination (5, 6, 7).