Human Papillomavirus: a vaccination update!
Via the New York Times, a story detailing the very recent recommendation by an advisory panel at the Centers for Disease Control to endorse vaccination against Human Papillomavirus (HPV) for boys ages 11 and 12. Currently, the CDC recommendation for the HPV vaccine (Gardisil) is for all girls at this age. The vaccine is designed to prevent infection by this very common, primarily sexually transmitted virus, which in turn is responsible for causing a significant number of cervical cancers in women. The move by the advisory committee would be followed up by a decision by the Director’s office at the CDC, with a likely recommendation to the Secretary of Health and Human Services presidential cabinet office for final approval.
The vaccine is currently rather expensive, at approximately $300 for the three dose regimen, however it is covered by most insurance programs at present. The Department of Health and Human Resources recommended in 2006 that girls be vaccinated by age 12 for HPV, and the vaccine is widely available, however the NYT article does note that so far compliance rates have been “disappointing,” suggesting a fair amount of public resistance. This negative perception has of course occurred in part due to public pronouncements by people such as Michelle Bachmann (see here for a rant from last month,) where she attributed a link between HPV vaccine and mental retardation.
Although the recommendation is likely to make it to full approval status resulting in a national recommendation for the HPV vaccine in both boys and girls, it is unclear to what extent it will make in cancer rates in the short term. Cervical cancer rates have been declining over the past few decades, even prior to the availability of an HPV vaccine, likely due to increased surveillance and early detection. However, as summarized here, forms of cancer (mouth and throat) attributable to HPV infection have been increasing in males very recently. These cancers would likely greatly diminish with common vaccination. And considering the cost of treating cancer (and hoping that you survive the disease,) the upfront $300 investment then seems like a real bargain.
I also came across this link via io9.com, which gives a current update on how the vaccine is constructed. Vaccines are typically made using two general approaches. In the first one, called attenuation, a virulent pathogen is manipulated in the laboratory to become avirulent, so that its ability to cause disease is diminished or eliminated. When the attenuated pathogen is introduced via vaccination, the immune system recognizes it at the bona fide pathogen, and generates a long term response that confers immunity to reexposure. This approach carries with it the danger that the attenuated pathogen reacquires virulence and then could potentially cause disease as a side effect. The “live” influenza vaccine and most current forms of polio vaccine are of this type, and the classic example of using cowpox to confer immunity to smallpox is the same thing in principle.
The second approach uses a killed pathogen, where the pathogen is grown in the laboratory and then is treated with chemicals to eliminate any chance that the pathogen can reacquire virulence. The killed pathogen still is able to induce a long term immune response, however there is no risk of getting the disease from this vaccine. The potential side effects are limited to adverse reactions to a vaccine component, such as the chemicals used to inactivate the pathogen. The flu “shot” is an example of this form of vaccine.
HPV vaccines such as Gardisil are using a new approach that wasn’t possible 10 or 20 years ago, where the genes of the pathogen are manipulated in the laboratory to make a novel kind of vaccine. In the HPV vaccine, individual virus components are assembled together in the lab by using the yeast Saccharomyces cerevisiae to make all of the virus pieces. For a virus to be infectious, it requires both a set of virus proteins (the capsid proteins) and a genome (nucleic acids that encode the instructions to make that virus.) In the case of the HPV vaccine, only the capsid proteins are present, and no genome is included in the virus-like particles that are included in the vaccine. This makes for vaccine preparation that effectively induces a long term immune response, has no risk of reacquiring virulence, and has not been treated with the chemicals that may be involved in adverse reactions to vaccine components.