Denmark is in a chronic baby shortage [1] and people in Western democracies are having less sex generally [2]. So, yay, less HPV. Go get vaccinated [3]. Unfortunately, there are some pretty significant (and sad, yes, sad) confounders.
Do you mean there is a causality between less sex and HPV vaccination, when you write “confounder”? I can’t find any study supporting this, hence double checking.
I think maybe they mean that the fact that people are having less sex is confounding the cause-effect relationship between vaccination and fewer cases of HPV. I don't know about people having less sex, though. That seems hard to believe.