A new study, published in the Journal of Infectious Diseases, provides new data regarding the effectiveness of the Human Papillomavirus (HPV) vaccine in reducing HPV prevalence.
The Advisory Committee on Immunization Practices (ACIP) started recommending routine Human Papillomavirus (HPV) vaccination in June 2006. In order to estimate the effectiveness of the HPV vaccine, researchers used data from the National Health and Nutrition Examination Surveys (NHANES), 2003-2006 and 2007-2010.
Here is the conclusion from the study: Within four years of vaccine introduction, the vaccine-type HPV prevalence decreased among females aged 14-19 years despite low vaccine uptake. The estimated vaccine effectiveness was high.
The study conclusion (drawn from the NHANES survey 2007-2010) was based on 740 girls, aged 14-19. However, only 358 were sexually active, and of those, only 111 had at least 1 HPV shot. If the study authors were trying to determine vaccine effectiveness, why did they include the girls who had not received a single HPV shot or did not report having sex?
An interesting fact that was not shared, was that among those 740 girls, the HPV prevalence of high-risk, non-vaccine types declined 20.7 percent (from 20.7 percent to 16.4 percent).
Table 1 from the journal article compares 1,363 girls, aged 14-19, in the pre-vaccine era (2003-2006) to all 740 girls in the post-vaccine era (2007-2010) regardless of sexual history or immunization status.
Table 3 narrows down the data to include only the sexually active girls. It then provides additional data to further compare the 111 vaccinated to the 239 unvaccinated girls (8 females without vaccination status).
In 2003-2006 (pre-vaccine era) it was estimated that 53.1 percent of sexually active girls, aged 14-19 had HPV. In 2007-2010, the overall prevalence of HPV in the same demographic declined by 19.2 percent to an overall prevalence of 42.9 percent.
Some healthcare professionals may be quick to assume that the HPV reduction was an obvious outcome after mass immunization. However, the data provided in Table 3 clearly demonstrates that the unvaccinated girls in this group had the best outcome. The study table separates the HPV prevalence into three categories: overall, vaccinated, and unvaccinated.
The overall prevalence of HPV in the study period 2007-2010 was 42.9 percent when the vaccinated and unvaccinated girls are combined. In 2007-2010, the overall prevalence of HPV was 50 percent in the vaccinated girls (14-19 years), but only 38.6 percent in the unvaccinated girls of the same age. Therefore, HPV prevalence dropped 27.3 percent in the unvaccinated girls, but only declined by 5.8 percent in the vaccinated group.
In four out of five different measures, the unvaccinated girls had a lower incidence of HPV. In the one instance where the unvaccinated girls had a 9.5 percent higher prevalence, there was a note under the table that read “relative standard error greater than 30 percent.” I suspect that the confidence interval values must have been extremely wide. Therefore, this particular value is subject to too much variance and doesn’t have much value.
I had a discussion about this study with one of the physicians that I work with, and this is what he had to say:
The percentage decrease is severely confounded by the number of unvaccinated girls that are included in the 2007-2010 group. It is not easy to isolate the effect of the vaccine when the 2007-2010 group is not stratified by vaccine status (those who were vaccinated and those who were not vaccinated). This would indicate poor design methodology and we must wait for a more authoritative study that uses improved methodology to make any conclusions.
This study left me with many unanswered questions. Do you think the ACIP should continue to recommend the HPV vaccine for all preteen girls and boys?