What are human papillomaviruses?
Human papillomaviruses (HPV) are a group of more than 100 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. 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 infection sometimes persists 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 HPV infections at some point, but very few will develop cervical cancer. The immune system of most women will usually suppress or eliminate HPV. Only HPV infections that are persistent (do not go away over many years) can lead to cervical cancer. In 2006, an estimated 10,000 women in the United States will be diagnosed with this type of cancer and nearly 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 also suggest that HPVs may play a role in cancers of the anus, vulva, vagina, and some cancers of the oropharynx (the middle part of the throat that includes the soft palate, the base of the tongue, and the tonsils). Data from several studies also suggest that infection with HPV is a risk factor for cancer of the 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.
Recently, the U.S. Food and Drug Administration (FDA) approved a vaccine that is highly effective in preventing persistent infection with HPV types 16 and 18, two “high-risk’ HPVs that cause most (70 percent) cervical cancers, and types 6 and 11, which cause virtually all (90 percent) genital warts.
What preventive HPV vaccines are available?
The FDA recently approved Gardasil™, a vaccine produced by Merck & Co., Inc. (Merck). It 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.
Another promising vaccine, Cervarix™, is produced and is being tested by GlaxoSmithKline (GSK), but is not yet approved by the FDA. This vaccine is called a bivalent vaccine because it targets two HPV types: 16 and 18. Early findings have shown that this vaccine also protects against persistent infection with these two types of HPV. It is also given in three doses over a 6-month period. Both vaccines are based on technology developed in part by National Cancer Institute (NCI) scientists. NCI 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, some of which cause cervical cancer. Therefore, about 30 percent of cervical cancers and 10 percent of genital warts will not be prevented by these vaccines. In addition, the vaccines do not prevent other sexually transmitted diseases, nor do they treat HPV infection or cervical cancer.
Because the vaccines will not protect against all infections that cause cervical cancer, it is important for vaccinated women to continue to undergo cervical cancer screening as is 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 HPV´s unique surface components might create an antibody response that is capable of protecting the body against infection, and these components could be used to form the basis of a vaccine. These surface components are virus-like particles (VLP) that are noninfectious and 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 the development of those cervical cell changes seen on Pap tests that may lead to cancer (2). Although these vaccines prevent HPV infection, it is not known if they can eliminate existing cervical cell changes due to HPV.
How effective are the HPV vaccines?
Gardasil and Cervarix are highly effective in preventing infection with the types of HPV that they target. FDA-approved Gardasil prevented 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.
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 take 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 the follow-up from abnormal Pap tests, thus helping to reduce health care costs and anxieties related to abnormal Pap tests and follow-up procedures (2).
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 thousands of people in the United States and many other countries. Thus far, no serious side effects have been noted. The most common problem has been brief soreness at the site of injection and other local injection site symptoms commonly experienced with other vaccines.
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. Studies thus far have shown that Gardasil can provide protection against HPV 16 for 4 years. Studies with Cervarix showed protection from infection with both HPV 16 and 18 for more than 4 years.
Will booster vaccinations be needed?
Studies are under way to determine whether booster vaccinations (supplementary doses of a vaccine, usually smaller than the first dose, that are given to maintain immunity) are necessary.
Who should get the HPV vaccines?
The vaccines are proven to be effective only if given before infection with HPV, so it is recommended that they be given before an individual is sexually active. The FDA´s licensing decision includes information about the age and sex for recipients of the vaccine. The FDA approved Gardasil for use in females 9 to 26 years of age.
Should the vaccine be given to people who are already infected with HPV?
The preventive vaccines currently under study do not treat infections, although they have been found to be generally safe when given to women who are already infected with
HPV.
Reference:
National Cancer Institute, USA.
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