HPV Vaccine Offers Cancer Protection, But for How Long?

Many people were shocked to learn that a virus was the cause of a deadly cancer that kills more than 5,000 American women each year: human papillomavirus, or HPV, is responsible for most cases of cervical cancer in the US. Even more surprising, scientists had created a vaccine that would protect women against four of the most important strains of the disease. The new vaccine, sold under the brand name Gardasil, was approved for use by the US Food and Drug Administration (FDA) in June of 2006.

HPV is extremely common, in fact, at least 20 million people in this country are already infected, according to the National Institutes of Health. It's estimated that there are more than 100 strains of HPV, but most of them are considered harmless. Thirty of these, however, are classified as either "low risk" or "high risk", depending on their potential effects on human health.

HPV prevention and treatment expert Fredrik F. Broekhuizen, MD, Medical College of Wisconsin Professor of Obstetrics & Gynecology, explains that together, two 'high risk' types of HPV - Types 16 and 18 - are responsible for 70% of all cases of cervical cancer in the US.

Two others, Type 6 and Type 11, cause up to 90% of genital warts. They are considered 'low risk'.

Gardasil protects girls and women from these four HPV types. It will not prevent the effects of existing HPV infection, but it will guard against any of the four HPV types that are not present prior to vaccination. If a patient already has HPV type 11, for example, the vaccine provides no benefit for type 11 but it will still protect against types 6, 16 and 18. (Another HPV vaccine will soon enter the market; it only works against HPV Types 16 and 18.)

Duration of Protection Unknown
For high-risk HPV, the vaccine has not been in use long enough to determine whether or not it offers 'lifetime' protection against cervical cancer. Many years can pass between viral infection and the onset of cervical cancer.

"For the current vaccine and for the one that will be entering the market, we know that as far as protection against development of pre-cancerous lesions of the cervix, if you give the vaccine before sexual activity starts, before a woman has had any exposure to HPV, so far it has been 100% effective," against HPV Types 16 and 18.

"But we don't really know yet how long that protection will persist," said Dr. Broekhuizen. "We're about eight years out from some of the early studies, so the questions still remain. Is the vaccine protective forever, or is it protective only for some limited period of time? Vaccination after exposure obviously gives less protection against cervical cancer down the road, because the HPV types that a person has been exposed to will still do to them whatever they were planning to do."

Because sexual activity (with or without intercourse) is the source of most HPV infections, "If you are vaccinated at age twelve, before most children are sexually active and exposed to HPV, we know that the vaccine protects for a good number of years but we cannot say at this point for how long. We may find out that a booster shot is needed some years later to offer continued protection."

"If you are twenty years old now and have been sexually active, you probably have been exposed to an HPV virus, but it is believed that vaccination with the currently-available vaccines will still offer between 30% and 40% reduction in risk for cervical cancer," says Dr. Broekhuizen.

Continuing Progress in Diagnosis and Treatment
Dr. Broekhuizen says that years of research have led to a deeper understanding of HPV, providing the groundwork for improvements in prevention and treatment. Tools such as Pap smears and other tests for cervical cancer have been available for years in the US, leading to better ways of eliminating genital warts and a steady decrease in cervical cancer deaths.

"It used to be that for the treatment of genital warts we would 'wait and watch' and sometimes the warts would disappear. If not, we would use somewhat destructive treatments like freezing or cautery (destroying them with heat) or excising them by cutting or with acid. There has been an ointment on the market for several years now, called Aldara, which modulates the patient's immune system so that it responds in a way that makes the wart disappear. There is more of that type of treatment used these days than destructive treatment.

"We used to think that if you had genital warts and we treated them, we would prevent the spread of the virus to your partner or we would prevent the spread of the virus to other areas where you would then have new warts. That concept was completely wrong. If you have the virus, it's there. It may go underground, or your body may suppress it, but making the warts disappear does not do anything to the presence of the virus elsewhere.

"Now we also know much better which patients we really have to worry about for risk of developing cervical cancer. We are probably giving less treatment for some of the precancerous conditions that we used to diagnose, because now we know that that it is more likely an infectious stage that may last for one or two years, and maybe we should simply wait for the right immune response. Those changes in understanding affect how abnormal pap smears are now dealt with in young patients."

Vaccine Could Result in Policy Changes
Because the vaccine does not protect against all types of HPV, it will not prevent all cases of cervical cancer or genital warts. Upon approval of the vaccine, FDA news releases pointed out that Gardasil does not protect against the less-common HPV types and said that "routine and regular Pap screenings remain critically important to detect pre-cancerous changes in the cervix to allow treatment before cervical cancer develops." But if the vaccine is given to enough young people for a long enough time, said Dr. Broekhuizen, much of that testing could be made more effective.

"In my mind the actual benefit of the vaccine is that it is probably in the long term a cost-effective way of modifying our current methods of screening for cervical cancer. There will be fewer abnormal Pap smears and this will allow us to adapt our evaluation and treatment of pre-cancers," said Dr. Broekhuizen. "If we only vaccinate 30% of the people, the impact on the total population will not be as great. We'll probably have to cover at least 80% of all 12-year olds for the next two generations to realize the overall benefit, to be able to say that we don't need to put resources into all those Pap smears, follow-up evaluations, and treatments that might be unnecessary or even harmful.

"If you look at the whole population, those who would benefit the most right now from the vaccine would be all the women in the world who at the moment have no access to what we have had access to for the last 50 years, tools such as Pap smears and scoping techniques and biopsies. In the US, what some call a racial disparity in cervical cancer deaths is really an access disparity. A higher percentage of African-American women here may die, but not because of race. The evidence shows that in the decades prior to their diagnosis, half of those who die of cervical cancer in the US had no screening or had inadequate screening."

Dr. Broekhuizen has done extensive work with public health providers in Africa and speaks regularly on HPV issues at international gatherings. He expressed concern that HPV vaccine will not be available in the short term to millions who need it unless basic changes are made in distribution. "The unfortunate reality is the current cost of the vaccine," he said. "They probably won't get it in the African countries that can't afford it.

"As a general matter of public policy, they're using the vaccines right now in Western Europe, where they base their decisions on health goals for the population as a whole. They do population screening; we do opportunistic screening when someone walks in to a doctor's office. Unless we have a health care system in which it is very easy to cover the whole population with vaccines, where there is easy access, HPV vaccines may very well become vaccines for the 'haves' but not for the 'have-nots'. Those who have higher risk factors will continue to have less access to the secondary prevention that must continue until the majority of the population is vaccinated."

Given the appropriate resources, notes Dr. Broekhuizen, the widespread use of HPV vaccines will have an impact not just within the US, but on the world as a whole.

Dan Ullrich
HealthLink Contributing Writer

Dr. Fredrik Broekhuizen practices at the Froedtert & The Medical College of Wisconsin Obstetrics and Gynecology Clinic and the Children's Hospital of Wisconsin Maternal-Fetal Care Center.

For more information on this topic, see the first part of Dr. Broekhuizen's article, HPV Vaccine Prevents Most Cervical Cancers and Genital Warts.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.