19 Jan, 15 | by Leslie Goode, Blogmaster
HPV is known to be the cause of various types of cancer, including cervical cancer. Routine vaccination before the onset of sexual activity ought therefore to be effective in reducing the incidence of these cancers, and has been adopted by many countries. The impact of such programmes will not be apparent for years; but the sharp reduction of cases of genital warts in several countries where vaccination has been introduced, is an encouraging indicator of the likely effectiveness of cancer prevention over the longer term (STI/blog/Smith & Canfell). Unfortunately, however, vaccination coverage has often been sub-optimal ( STI/Sacks & Robinson). A number of recent contributions to STIs have attempted to identify parental (and provider) concerns that may be responsible for poor uptake of vaccination (STI/Schuler & Brewer; STI/Javanbakht & Guerry; STI/Krupp & Madhivanan).
One concern frequently mentioned by these studies is that HPV vaccination could lead to sexual disinhibition. The results of a large population-based cohort study in Canada (Smith & Levesque (S&M)), where HPV vaccination was introduced in 2006, may help to offer some assurance on this matter. The study was based on administrative health data relating to a cohort of 260,493 girls, of whom approximately half were in the first two school year-groups offered the vaccine (2006-7; 2007-8), and the other half in the previous two year groups (2004-5;2005-6). The study compared data from the two groups in respect to the incidence of pregnancy and non-HPV-related STIs over the four years following vaccination. Earlier studies addressing the question of vaccination-related disinhibition have focussed on risk perception or reported sexual behaviour. S&M use objective medical outcomes – pregnancy and STi diagnoses. Moreover, the definition of the groups on the basis of eligibility for vaccination, as opposed to vaccination itself, circumvents the potential confounding bias which might have been expected to arise from the fact that the same beliefs and behaviours influencing the decision to vaccinate would likely also have affected the outcome of pregnancy and STI infection.
The results are entirely reassuring. In respect to pregnancy they show precisely no difference between the eligible as opposed to ineligible girls (RR = 1.0 0); in regard to non-HPV related STI diagnoses, they show a small reduction among eligible girls, which the authors plausibly attribute to the likely eventuality of some HPV-related warts having being categorized in the data as non-HPV-related. These findings corroborate, on a population wide basis, those of earlier studies (e.g. Bednarczyk & Omer) which indicate that fears of vaccination-related disinhibition are unwarranted.