HPV vaccine

From Wikipedia, the free encyclopedia

This article documents a current event.
Information may change rapidly as the event progresses.

Human papillomavirus (HPV) vaccine is a vaccine designed to immunize against certain sexually transmitted diseases, such as cervical cancer and genital warts, which are caused by human papillomaviruses. The only HPV vaccine currently on the market is Gardasil, with a second vaccine, Cervarix, currently in clinical trials.

1 Introduction
2 Target populations
3 Implementation
4 History of HPV vaccines
5 Controversy
6 Therapeutic HPV vaccines
7 References
8 External links

[edit] Introduction

Of the more than 120 known HPV types, 37 are known to be transmitted through sexual contact. Infection with sexually transmitted HPVs is very common in adult populations worldwide. Although a few HPVs, such as types 6 and 11, can cause genital warts, most genital HPV infections come and go without ever causing any symptoms. However, lingering infections with a subset of about 19 "high-risk" HPV types can lead to the development of cervical cancer or other genital/anal cancers.^[1]

The latest generation of preventive HPV vaccines are based on hollow virus-like particles (VLPs) assembled from recombinant HPV coat proteins. The vaccines target the two most common high-risk HPVs, types 16 and 18. Together, these two HPV types cause about 70 percent of all cervical cancer. Gardasil also targets HPV types 6 and 11, which together cause about 90 percent of all cases of genital warts.^[1]

Gardasil and Cervarix are designed to elicit virus-neutralizing antibody responses that prevent initial infection with the HPV types represented in the vaccine. The vaccines have been shown to offer 100 percent protection against the development of cervical pre-cancers and genital warts caused by the HPV types in the vaccine, with few or no side effects. The protective effects of the vaccine are expected to last a minimum of 4.5 years after the initial vaccination.^[2]

While the study period was not long enough for cervical cancer to develop, the prevention of these cervical precancerous lesions (or dysplasias) is believed highly likely to result in the prevention of those cancers.^[3]

Although a 2006 study suggests that the vaccines may offer limited protection against a few HPV types that are closely related to HPVs 16 and 18, it is clear that other high-risk HPV types can circumvent the vaccines.^[2] Ongoing laboratory research is focused on the development of HPV vaccines that will offer protection against a broader range of HPV types. There is also substantial research interest in the development of therapeutic vaccines, which seek to elicit immune responses against established HPV infections and HPV-induced cancers.

[edit] Target populations

Gardasil and Cervarix are preventive (rather than therapeutic) vaccines, recommended for women who are 9 to 25 years old and have not contracted HPV. However, since it is unlikely that a woman will have already contracted all four viruses, and because HPV is primarily sexually transmitted, the US Centers for Disease Control and Prevention has recommended vaccination for women as old as 26.

Although HPV types 6 and 11 do not cause cervical cancer, they can cause genital warts. "Warts cause considerable discomfort and psycho-social trauma, so this makes the vaccine more attractive and also provides a reason other than altruism for men to be immunized," explains John Schiller of the National Cancer Institute.^[4] HPV also causes anal and penile cancer. In the UK the drug is licensed for girls and boys aged 9 to 15 and for women aged 16 to 26. Thus, the drug has to be administered to men "off license".^[5]

[edit] Implementation

In developed countries, the widespread use of cervical "Pap smear" cancer screening has dramatically reduced the incidence of invasive cervical cancer. Since the current generation of preventive vaccines will not protect against all the HPV types that can cause cervical cancer, it will be important for women to continue to seek regular Pap smear screening, even after vaccination.

Pap smear screening is too expensive for routine use in developing countries and HPV-induced cervical cancer remains the fifth most common cancer in women worldwide.^[6] Thus HPV vaccines are most urgently needed in developing countries. With a cost of $360, Gardasil is the most expensive vaccine ever developed. The vaccine will be too expensive for initial use in developing countries unless substantial subsidies are offered. Merck has announced that it intends to support programs to offer Gardasil to disadvantaged women worldwide.^[7] The Bill & Melinda Gates Foundation has also expressed interest in helping make preventive HPV vaccines available to women in developing countries. Through the PATH organization, a nonprofit organization whose mission is to improve the health of people worldwide by advancing technologies, the Gates Foundation has donated $27.8 million to implement HPV vaccines. Starting in January 2007, women in India, Peru, Uganda and Vietnam will be receiving the vaccine.

[edit] History of HPV vaccines

The vaccine was developed in parallel by researchers at Georgetown University Medical Center, the University of Rochester, Queensland University in Australia, and the U.S. National Cancer Institute. Intellectual property resulting from the discovery has been contentious. Following over 10 years of adjudication, the European Patent Office awarded the controlling patent for the cervical cancer vaccine to the University of Rochester. Following this, the U.S. Patent Office recognized Georgetown University as having the dominant patent claim in the United States, based on filing date.^[8] ^[9]

In 2006, the U.S. Food and Drug Administration approved the first preventive HPV vaccine, marketed by Merck & Co. under the tradename Gardasil. Early in 2007, GlaxoSmithKline is expected to seek approval in the United States for a similar preventive HPV vaccine, known as Cervarix. In the European Union, GlaxoSmithKline filed the application for approval in March 2006.

[edit] Controversy

Several U.S. states have considered mandatory HPV vaccinations; however, as of February 2007, only the state of Texas requires HPV vaccinations for girls. At least 18 other states and the District of Columbia have considered similar policies.^[10]

Texas Governor Rick Perry, without legislative approval, issued an executive order on 2 February 2007 mandating Gardasil be given to all school girls entering sixth grade, beginning September 2008. Adding to the criticism of Perry's order is Merck's campaign contributions to Rick Perry and what is viewed by some as a high price of the vaccine which is approximately $US360 in Texas.^[11] It being a patent-protected vaccine, Merck is the sole producer of Gardasil.

Several conservative groups in the U.S., who are in favor of the vaccine, have publicly opposed the concept of making HPV vaccination mandatory for pre-adolescent girls, citing that making the vaccine mandatory is a violation of parental rights. Both the Family Research Council and the group Focus on the Family expressed concerns about this.^[12]^[13]

Some individuals and groups have raised similar objections to the HPV vaccine that have been raised to other vaccines (see vaccine controversy).

[edit] Therapeutic HPV vaccines

In addition to preventive vaccines, such as Gardasil and Cervarix, laboratory research and several human clinical trials are focused on the development of therapeutic HPV vaccines. In general these vaccines focus on the main HPV oncogenes, E6 and E7. Since expression of E6 and E7 is required for promoting the growth of cervical cancer cells (and cells within warts), it is hoped that immune responses against the two oncogenes might eradicate established tumors.^[14]