HPV Vaccine Won"t Help Clear Existing Infection

By Rachael Myers Lowe, cancerpage.com

(August 15,  2007 ) - In the fight against cancer, vaccines take on a new role. They are being investigated to marshal the body’s defenses against an existing cancer but success has been limited.

A conventional vaccine has been approved by the federal government against a virus that causes cervical cancer.  The human papilloma virus (HPV) vaccine has proved effective in preventing infection by two of an estimated 25 HPV strains that can cause cervical cancer to develop.  

Researchers at the National Cancer Institute and in Costa Rica wondered if the vaccine, in additional to the government approved use to prevent infection in the first place, would be useful as a therapy to clear the body of the virus after a woman was infected.

They enrolled nearly 2200 HPV positive women aged 18 to 25 in a clinical trial to randomly receive either the HPV vaccine or hepatitis A vaccine.  The women were then tested for HPV infection at 6 months, and at 12 months.

The research team found no evidence that the HPV vaccine had any effect on clearing the virus from the women’s systems. Clearance rates of HPV-16/18 infection at 6 months were 33.4% in the HPV vaccine group and 31.6% in the HEP A control group.  At 12 months, rates were 48.8% and 49.8%, respectively.

As a result, research leader Dr.  Allan Hildesheim of the National Cancer Institute tells cancerpage, the findings “reinforce the need to vaccinate adolescent girls before they initiate sexual activity and before they become exposed and infected with the virus.”

 In addition, there’s no evidence to suggest that the vaccination, given after infection, has any therapeutic value so it should not be given in an attempt to treat the infection.

“If you have an abnormal pap smear and test HPV positive, you should not be taking this vaccine to try to treat that lesion, that won’t work”, Dr. Hildesheim said.

Many other questions remain to be answered about the HPV vaccine before the best population to be vaccinated can be better defined.  For instance, “the evidence is not there yet to justify large scale vaccination programs for older women who are sexually active,” Dr. Hildesheim said.

Given the high cost of the vaccine, as much as $375 for the series of three shots, perhaps women should be tested for HPV before given the vaccine.  Dr. Hildesheim does not agree.

“Pre-testing before vaccination would not be a good idea because it’s not just a matter of knowing that they have the infection today or not but also knowing what their past history is and there’s no way  to define that,” he said.

If a woman has already been infected and cleared the virus on her own, and most women do, should she still get the vaccine to protect her from an infection down the road?

“We can’t say that, we can’t prove that or negate that -- we need more time and data before we can make that determination,” Dr. Hildesheim said.

SOURCE: 

• Journal of the American Medical Association 2007; 298: 743-753.
• Cancerpage.com telephone interview with Dr.  Allan Hildesheim on 8-14-07