how do you assess the impact of the hpv vaccine?

Question: how do you assess the impact of the hpv vaccine?
- Keywords:
  hpv,
  impact,
  vaccine
Asked by les science est tres cool to Kevin on 15 Jun 2017. This question was also asked by 933epdj46.
- Kevin Pollock answered on 15 Jun 2017:
  
  We look at women who come forward for their first smear and take a small sample of their cells, where we can look for HPV in the cells. In Scotland, we can link these cells to the woman to see if she was vaccinated then compare the prevalence of virus between immunised and non-immunised women. we have seen a 90% reduction in high-risk HPV, the type most likely to cause cancer. This is strongly suggestive that the vaccine is working.

Question: how do you assess the impact of the hpv vaccine?