Whack-A-Mole for HPV Vaccine

HPV vaccine with certain strains does not lead other strains to proliferate

(RxWiki News) Sometimes medicine is kind of like a game of whack-a-mole. You whack down one thing, and then another pops up. Some scientists have been worried that could happen with HPV.

There is an HPV vaccine, but it only covers some of the strains of the sexually transmitted virus.

Would vaccinating everyone cause the other strains to become more common? A research study offers evidence that this may be unlikely with HPV.

"The HPV vaccine works - ask your doctor."

HPV stands for human papillomavirus, a very common sexually transmitted infection that causes cervical cancer. It can also lead to other cancers of the mouth, throat, anus and penis.

The US Centers for Disease Control and Prevention recommend the HPV vaccine for boys and girls. There are two vaccines: Gardasil and Cervarix.

Gardasil protects against the strains HPV 16, HPV 18, HPV 11 and HPV 6, and Cervarix protects only against HPV 16 and HPV 18, which are the two strains that cause cervical cancer.

One concern has been that other strains of HPV may become more common if the HPV 16 and HPV 18 became less common because of vaccination.

But a study led by Anne Rositch, of the Department of Epidemiology at the University of North Carolina in Chapel Hill and at the John Hopkins Bloomberg School of Public Health, suggests that may not be the case.

The study involve 1,097 men in Kenya who are involved in a larger medical trial related to circumcision.

Circumcision has been used in Africa to reduce the transmission of sexually transmitted diseases such as HPV.

These men were not vaccinated against HPV, but many of them already had one or more strains of HPV at the start of the study, and many became infected with other HPV strains during follow-up.

The researchers looked at who had HPV 16 and HPV 18, as well as other strains, at the start of the study and who contracted them during the study.

They then did some calculations to determine if any of the men contracted certain HPV strains more quickly based on what already existed in the population.

They found that there was no difference in how long it took for the men to contract HPV strains, regardless of which ones they already had.

This study deals with association only, and it did not deal with vaccinated people, so the findings are limited.

However, the mathematical calculations offer evidence that other HPV strains are unlikely to become more common if the ones that cause cancer are decreased through vaccination.

"These prospective data on combinations of HPV infections over time do not suggest the potential for post-vaccination HPV type replacement, the authors wrote. "Future surveillance studies are needed to definitely determine whether elimination of HPV types by vaccination will alter the HPV type distribution in the population."

The senior author of the study, Jennifer Smith, PhD, MD, an associate professor of epidemiology at the UNC Gillings School of Global Public Health, explained this means the amount of one strain of HPV that exists doesn't affect the amount of another strain.

"Our findings are of potential importance because they suggest that HPV types are generally acting independently from one another," she said.

"Thus it is unlikely that HPV type-replacement will occur following large scale vaccination programs of young male adolescents."

The study was published June 18 and appears in the September issue of The Journal of Infectious Diseases. The research was funded by the National Cancer Institute, the National Institutes of Health, the University of North Carolina Center for AIDS Research and the Canadian Institutes of Health Research.

One author has received speaker fees from and served on the advisory board of the pharmaceutical company GlaxoSmithKline, which manufactures the HPV vaccine Cervarix.

Another author has received grants and consultant fees from GlaxoSmithKline and from Merck, which manufactures the other HPV vaccine Gardasil. The other authors declared no conflicts of interest. Image courtesy of Bob Space Racers.

Review Date: 
August 28, 2012