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Monday, January 12, 2009

The Human Papilloma Virus (HPV), Gardasil, and Cancer: What are the connections and should young boys be vaccinated too?

Gardasil, Merck's vaccine against the Human Papilloma Virus (HPV), has been in the news again recently with the announcement that they are seeking FDA approval to expand its use to include males ages 9-26 years old. This has reopened the discussion about HPV and how aggressively we should fight to eradicate this virus.
HPV (Human Papilloma Virus) is the most common sexually transmitted disease in the US. Yet most people are never even aware that they have been infected. The CDC (Center for Disease Control) estimates that about 6.2 million people are infected with genital HPV every year. Eighty percent of women will have acquired genital HPV by the time they reach 50 years old. Even more alarming are the statistics for young Americans. In 2000, there were 4.6 million new cases of HPV infection in 15-24 year olds. To put that in prospective, in the same age group, there were only 7,500 new cases of Hepatitis B and 8,200 of Syphilis.
To understand the significance of HPV, one must first understand the natural course of the virus. Of the 6.2 million people infected with HPV annually, 90% will clear the infection on their own within 2 years. However, if a woman’s body does not clear the infection, there is the potential for cervical cancer to develop. The progression to cervical cancer is slow, usually 10-15 years or more after the initial infection. Prior to cervical cancer developing, there are changes in the cells and tissue of the cervix. These changes are screened for with a Pap smear. In the U.S., there is an intense screening protocol that recommends women receive Pap smears every 1-3 years. Abnormal Pap smears are followed up with additional tests and if changes in the cervical cells are confirmed, the tissue is removed or destroyed in an attempt to prevent a progression to cancer. Although cervical cancer is the second most common cancer in women worldwide, the rigorous screening protocol in the U.S. has limited the amount of deaths to 3000-4000 annually.
Gardasil, which was approved by the FDA in June of 2006 for use in females 9-26 years old, is a vaccine against four strains of HPV -- HPV types, 6, 11, 16 and 18. There are over a hundred types of HPV but the vaccine is designed to vaccinate only against types 6, 11, 16, and 18, which are the major disease causing types. Types 6 and 11 cause 90% of genital warts and types 16 and 18 cause 70% of cervical cancer. HPV types 16 and 18 have also been implicated in anal, penile, oropharyngeal (mouth and throat), vulvar and vaginal cancers. Thus, the vaccine may protect against these cancers as well.
There is still much hesitation surrounding Gardasil. As a parent, it is often difficult to wade through all the news reports and information out there in order to ultimately decide if this vaccine is right for your child. With any vaccine, there are certain questions that need to be answered. For Gardasil the questions are, "Is it safe, is it effective and will the protection against HPV last throughout her adult lifetime?"
All new vaccines are just that, new. As time goes on and more girls are vaccinated without serious adverse effects, we will become more comfortable that the vaccine is safe. Gardasil was tested by Merck before its release and has been approved by the FDA (Food and Drug Association) but still the number of girls that have been, and will be, immunized since the release of the vaccine far outnumbers those observed in the clinical trials. Once a vaccine is released to the public, a government database collects information on any adverse effects people are experiencing and if needed additional warnings are added to the vaccine's packaging. Since Gardasil's release, its warning has been modified to include joint and muscle pain, fatigue, physical weakness and general malaise.
Is the vaccine effective? It has been shown to be 100% effective against cervical cancer caused by HPV 16 and 18, and 99% effective against genital warts caused by HPV types 6, 11. Of course, it can’t be effective if a person has already acquired an HPV infection of type 6, 11, 16 or 18. It is a vaccine, not a treatment. So, it is critical to vaccinate prior to acquiring an infection. Since HPV is a sexually transmitted disease, it is best if girls are vaccinated prior to their first sexual experience. But at what age does the typical American girl become sexually active? The US National Health and Nutrition Examination Survey found that the occurrence of HPV in girls 14-19 years old was 24.5%. That number jumped to 44.8% for girls 20-24 years of age. That means that about 1 in every 4 girls leaving high school and almost 1 in every 2 girls leaving college would be infected with HPV. Therefore, the current recommendation is to vaccinate girls at 11-12 years of age in order to hopefully vaccinate them before they acquire the disease.
There is of course the concern that the effectiveness of the vaccine will wear off over time. This is the reason that some vaccines require booster shots. The studies released thus far show that the vaccine is effective up to 5 years post vaccination. Of course, the hope is that the vaccine will protect a women though her adult lifetime. There are on going studies to evaluate Gardasil's continued effectiveness and if a booster is deemed necessary, one will be added to the vaccination schedule.
Less than three years after Gardasil's emergence and the commencement of these questions, new questions are now surrounding the vaccine and its potential use. Should it be given to males?
It stands to reason that if you are trying to eradicate a disease you want to vaccinate the carriers of the virus as well, in this case, young men. The vaccine would have some benefit men as it would protect them against genital warts as well as some very rare cancers: oropharyngeal, anal and penile cancers. However, the main reason to vaccinate men is to decrease the risk of them giving the virus to women. The US would not be the first country to approve Gardasil's use in males. Australia, Mexico and countries in the European Union have already done so. We will have to wait and see what the FDA does. For now, Gardasil is only available for girls.