Reply to "HPV vaccine requirements, opt-outs and providers' support: key studies missing from a recent systematic review".

The peer-review process represents a crucial step in improving the quality of published research. Nevertheless, after it, there could be room for further improvements. In this case, concerns about the sensitivity and sensibility of the search strategy used in a recently published review were raised. With this letter we address the issues raised, being aware, as stated in the paper that "The results of the review could serve as a starting point for further studies analyzing these aspects". In light of this, the present paper could be the opportunity to start cooperation to better assess the parents' attitudes towards HPV vaccine requirements.