HPV Infection Rate Down After Vaccine Approval

The prevalence of infection with cancer-causing strains of human papillomavirus (HPV) declined among women during the period that coincided with the introduction of HPV vaccine, investigators reported here.

The rates of infection with HPV 16 and HPV 18 have declined since July 2007, a year after the first vaccine was introduced, including a significant decrease in HPV 16 infection (P=0.0012).

Four other HPV subtypes, including the other two targeted by the quadrivalent vaccine (Gardasil), also declined significantly. Overall, the rate of infection with any HPV subtype has decreased since mid-2007 among, according to HPV test results for 57,262 women.

Because the women’s vaccination status was unknown, the decline could not be linked definitively to the vaccines, Elizabeth Dickson, MD, said at the Society of Gynecologic Oncology meeting.

“[The decline] could be because of the vaccine,” Dickson, of the University of Minnesota in Minneapolis, told MedPage Today. “It could just be that the natural history of the HPV types is changing and that the milieu of the types of HPV in women’s samples is changing over time.”

What is genital HPV infection?
Genital human papillomavirus (also called HPV) is the most common sexually transmitted infection (STI). There are more than 40 HPV types that can infect the genital areas of males and females. These HPV types can also infect the mouth and throat. Most people who become infected with HPV do not even know they have it.

HPV is not the same as herpes or HIV (the virus that causes AIDS). These are all viruses that can be passed on during sex, but they cause different symptoms and health problems.

“But it’s an interesting finding because, even though we didn’t know their vaccination status, the HPV types in the vaccine are going down,” she said.

- This study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
- The prevalence of infection with cancer-causing strains of human papillomavirus (HPV) declined among women during the period that coincided with the introduction of HPV vaccine.
- Four other HPV subtypes, including the other two targeted by the quadrivalent vaccine (Gardasil), also declined significantly.

According to the CDC, about 40 types of HPV have been linked to genital infection. Interest in individual HPV strains has increased because of recognition that specific strains are more closely associated with cervical cancer (HPV 16 and 18) and with genital warts (HPV 6 and 11) than are other subtypes.

Numerous studies have documented the uptake of the HPV vaccines, but information about temporal trends in HPV infection with specific strains has been scarce.

Dickson and colleagues sought to document patterns of HPV infection, focusing on the 18 most prevalent types. They analyzed specimens obtained from women who participated in cervical cancer screening programs (including HPV testing) during 2004 to 2011. Participants’ ages ranged from 11 to 29 at the time of testing.

How do people get HPV?
HPV is passed on through genital contact, most often during vaginal and anal sex. HPV may also be passed on during oral sex and genital-to-genital contact. HPV can be passed on between straight and same-sex partners - even when the infected partner has no signs or symptoms.

A person can have HPV even if years have passed since he or she had sexual contact with an infected person. Most infected persons do not realize they are infected or that they are passing the virus on to a sex partner. It is also possible to get more than one type of HPV.

Rarely, a pregnant woman with genital HPV can pass HPV to her baby during delivery. Very rarely, the child can develop juvenile-onset recurrent respiratory papillomatosis (JORRP).

Using test results provided by three clinical laboratories, investigators estimated the prevalence of type-specific HPV infection in 3-month increments over the entire study period. Additionally, they compared type-specific infection rates before and after introduction of the first HPV vaccine.

To allow for uptake and completion of the vaccine series, the “after” period began approximately a year after the vaccine became available.

The age of the women averaged about 24 in the periods before and after the vaccine.

HPV Vaccines

HPV vaccines are given as three shots to protect against HPV infection and HPV-related diseases. Two vaccines (Cervarix and Gardasil) have been shown to protect against most cervical cancers in women. One vaccine (Gardasil) also protects against genital warts and has been shown to protect against cancers of the anus, vagina and vulva. Both vaccines are available for females. Only Gardasil is available for males.

HPV vaccines offer the greatest health benefits to individuals who receive all three doses before having any type of sexual activity. That’s why HPV vaccination is recommended for preteen girls and boys at age 11 or 12 years.

Overall, the rate of infection with any of the 18 HPV types declined slightly. The investigators also found that the number of HPV tests increased during each 3-month interval across the study period.

Using regression models to predict infection rates before and after July 2007, Dickson and colleagues found significant differences between the two periods for 6 HPV types:

  HPV 6 (P<0.0001) HPV 11 (P=0.0260) HPV 31 (P=0.0126) HPV 59 (P=0.0477) HPV 8 (P=0.0028) HPV 16 (P=0.0012)
Infection rates declined more rapidly after July 2007 for all but HPV 68, which stabilized following an earlier decline. Moving the start point a year in either direction produced similar results. Regardless of the explanation for the change in HPV infection rates, the shift “may prove to be an important factor in future trends in rates of Cervical dysplasia and cancer,” Dickson said.
Dickson and co-investigators had no disclosures.
Primary source: Society of Gynecologic Oncology Source reference: Dickson E, et al “Changes in type-specific HPV infection rates in the United States” SGO 2012; Abstract 87.

Provided by ArmMed Media