Taking stock and looking ahead: Behavioural science lessons for implementing the nonavalent human papillomavirus vaccine.

The development and licensing of a nonavalent human papillomavirus (HPV) vaccine has the potential to reduce morbidity and mortality from HPV-related cancers beyond that of first generation HPV vaccines. However, this benefit can only be realised if the offer of vaccination is accepted. Uptake of first generation HPV vaccines is not complete and shows huge global variation. In addition to practical and financial challenges to optimising coverage, behavioural issues explain a large proportion of the variance in vaccine receipt. This commentary draws on the findings of over a decade of behavioural science research seeking to understand uptake of first generation HPV vaccines, in order to anticipate challenges to implement the nonavalent HPV vaccine. Challenges include distrust of combination vaccines, uncertainty about long-term efficacy, distrust of a new and (perceived to be) untested vaccine, cost and uncertainty regarding interchanging doses of first generation and nonavalent vaccines and the appropriateness of revaccination. We use behavioural science theory and existing evaluations of interventions to increase uptake of vaccines to identify evidence-based approaches that can be implemented by vaccine stakeholders to address parents' concerns and maximise uptake of the nonavalent HPV vaccine.