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'How likely am I to get an HPV infection?'

Dr. Judith Reichman on the HPV virus and its connection to cervical cancer.
/ Source: TODAY

Q: I'm 22 years old and am sexually active. I've been told by my doctor, my mother, and the ads on TV and in magazines to get Gardasil (the HPV immunization). How likely am I, though, to actually get an HPV infection?

A: You're right, there's an enormous effort currently underway to get women to understand the connection between HPV (Human Papilloma Virus) and cervical cancer. High-risk types of HPV cause 99 percent of cervical cancers, and 70 percent of these cancers are due to two specific types (number 16 and 18). The new HPV vaccine (called Gardasil) not only guards against 16 and 18, it also protects against two other HPV types – 6 and 11 which cause genital warts.

The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices (ACIP) currently recommends that Gardasil be given to adolescent girls who are 11 and 12 years old, and suggest “catch up” vaccination for young women between the ages of 13 and 26. (Most women in this latter age group will need this “catch up”, since the vaccine is new and wasn’t available when they were younger). We're not yet sure what women over the age of 26 should do;  studies have not been completed regarding the benefit of immunization in this age group.  Since you are 22, you fit the profile for the Gardasil vaccine. It’s given as three shots over a time period of six months.

Now to answer your question about your actual chances of getting and HPV infection. To answer this we need to look at prevalence studies. Prevalence (and here I have to give a scientific definition) is the proportion of old and new cases of a condition (or in this case an infection) which are present at a single point in time in a certain population. The largest study looking at the prevalence of HPV was reported in the Journal of the American Medical Association (JAMA) at the end of February. It's called the National Health and Nutrition Examination Survey (NHANES), which is a national survey performed on a regular basis.

For the survey, 1,921 women provided a self-collected vaginal swab (they inserted a tampon-like swab and then pulled it out), which was then examined for HPV. The women ranged in age from 14 to 59 and were felt to reflect the ethnic, socioeconomic and marital status of women in the U.S. in this age group. They were also given a questionnaire regarding their sexual activity, number of past partners, recent partners, and educational background.

Statisticians then figured out the prevalence of HPV based on the self-collected and tested swabs. Here are the results: The overall prevalence of HPV infection (any type of HPV and there are more than 30 types) was 26.8 percent. However, the prevalence was 44.8 percent (nearly half) among women between the ages of 20 and 24 while one third of women between the ages of 14 and 24 had HPV. When translated into actual numbers, this means that 7.5 million females have an HPV infection, which makes this the highest level of STDs ever documented.

The overall prevalence of the high-risk types of HPV (the ones we feel are more likely to cause cervical cancer) was 15.2 percent and that of low-risk HPV was 17.8 percent. The researchers also looked at the prevalence of the four types of HPV targeted by the vaccine (16, 18, 11, and 6). All four of these HPV types were found in 3.4 percent of the women and the combined prevalence of the two high-risk types of HPV that cause cervical cancer (16 and 18) was around 2 percent. At least one of these four HPV types was found in 6 percent of women 14 to 19 years old, which would indicate that it's most helpful to get to these girls before they "catch" the virus.

Finally, the survey showed that most of the women infected only had one type of HPV, 23 percent had two types, and 16 percent had three types or more. 

The authors of the study pointed out that since they only had two years of data, additional years and a bigger sample size could change the number and types of HPV found. They also added that previous studies of HPV prevalence showed a higher antibody presence in the blood and that these antibodies might provide a better idea of the cumulative (past and present) exposure to HPV in women in this age group. (The reason there is a difference between viral secretion results and those found with antibody testing is, that over time, viral secretion can cease. It’s thought that only those women with ongoing active viral activity are at high risk for developing cervical cancer, while those who were merely exposed and whose virus “burned itself out” are much less likely to be at risk….thank goodness!).

These prevalence studies give us a glimpse at the mathematical probability that you or another sexually active woman in your age group will become infected with HPV. The overall numbers are quite impressive, but the chance of becoming infected with the particular strains that are targeted by this vaccine is still fairly small. Is it enough to warrant the cost of the vaccine? (It’s currently $120 per shot and you need 3 shots to complete the vaccination). I would like to think that even 6 percent is too high. Some States are trying to pass laws to make the immunization mandatory. (Texas already has.)  But more studies are needed before we decide to use available economic resources to vaccinate all girls (and since the virus is spread through sexual contact there is a gender issue as to whether we should also vaccinate boys….boy this is becoming complicated!)  In the meantime, I  do offer Gardasil immunization to all my patients who are at or under the age of 26.

Dr. Reichman’s Bottom Line: It's exciting that we not only know what causes cervical cancer, but can also take steps to prevent it. Your individual chance of becoming infected with one of the HPV viruses is quite high, less so for the virus that is targeted by Gardasil. But why take a chance?  If you are sexually active (or plan to become so) get the vaccine… And don’t forget there are many more HPVs and STDs out there… so you need to continue to use condoms and get regular PAP smears.

Dr. Judith Reichman, the TODAY show's medical contributor on women's health, has practiced obstetrics and gynecology for more than 20 years. You will find many answers to your questions in her latest book, "Slow Your Clock Down: The Complete Guide to a Healthy, Younger You," which is now available in paperback. It is published by William Morrow, a division of .

PLEASE NOTE: The information in this column should not be construed as providing specific medical advice, but rather to offer readers information to better understand their lives and health. It is not intended to provide an alternative to professional treatment or to replace the services of a physician.