Understanding the Determinants of Vaccine Hesitancy and Vaccine Confidence among Adolescents: A Systematic Review

"In order to make it possible to implement effective actions counteracting VH [vaccine hesitancy], the understanding of its determinants is of utmost importance."

Vaccine uptake among adolescents aged 10-19 is low, even though they make up 25% of the global population. Vaccine hesitancy (VH), ranging from delay in vaccination to selective rejection of certain vaccines to complete refusal, has not been widely studied in this population. This systematic review seeks to identify the main reasons behind VH and vaccine confidence among adolescents, including vaccine-/vaccination-related issues and individual and contextual factors. This information may be useful to inform tailored interventions for the promotion of vaccination among adolescents.

A systematic review was conducted and reported according to the Preferred Reporting Items for Systematic Reviews (PRISMA). PubMed, Scopus, and Web of Science were searched from inception until December 11 2020 for articles in English assessing adolescents' attitudes toward vaccination in terms of hesitancy and/or confidence. Of 14,704 articles, 20 studies were included in the qualitative analysis. Included articles were published from 2010 to 2020. Most of the articles included in the review dealt with human papillomavirus (HPV) vaccination, but 35% addressed other vaccines, such as hepatitis B, tetanus, diphtheria, pertussis, measles, mumps, rubella, varicella, meningococcal diseases, influenza, and pneumococcal diseases.

Selective findings:

• Knowledge of vaccine-preventable diseases and associated risks, together with the awareness of available vaccines and the availability of correct information about them, positively influenced adolescents' vaccine acceptance.
• Concerns about the potential side effects deriving from the vaccine and the lack of detailed information about them are described as two of the main reasons underlying VH in the adolescent population.
• The family and school environment as information sources seem to have a positive impact on adolescents' attitude toward vaccinations. The least reliable, though most easily accessible, source of information on vaccines was social media.
• In some cases, having different options to access the vaccine (e.g., school, free clinics, etc.) is a factor that positively affects confidence in vaccination programmes and also leads to an increased uptake.
• One study reported that the fear of the needle and the pain due to the injection are potential discouraging factors, and combined vaccines are significantly preferred, since they reduce the overall number of injections.
• Adolescents seem to prefer taking an active part in the decision-making process, but they also appreciate the support and the guidance of healthcare professionals or their parents.

Based on the findings of the review, the researchers make several recommendations, such as considering the role the school context has to play in bolstering students' vaccine literacy and building their confidence in vaccines. In fact, previous research provides evidence that educating students through school-based educational programmes represents one of the best practices to promote vaccine awareness among adolescents.

Per the researchers, future studies could further disentangle the role of VH determinants and their interrelationships and investigate how VH and its determinants influence final vaccination uptake, considering also other issues, such as access and affordability.

In conclusion, because adolescence is a phase of life in which boys and girls begin to make significant choices in respect to their health and develop attitudes and behaviours that remain in adulthood, "Improving adolescents' vaccination uptake can provide substantial health benefits to individuals, society, and future generations."