Abstract: We included 16 studies (eight individually randomised trials, four cluster randomised trials, three non-randomised trials, and one controlled before-after study). Twelve studies were conducted in the USA, while there was one study each from: Australia, Sweden, Tanzania, and the UK. Ten studies had unclear or high risk of bias. We categorised interventions as recipient-oriented, provider-oriented, or health systems-oriented. The interventions targeted adolescent boys or girls or both (seven studies), parents (four studies), and providers (two studies). Five studies had mixed participants that included adolescents and parents, adolescents and healthcare providers, and parents and healthcare providers. The outcomes included uptake of human papillomavirus (HPV) (11 studies); hepatitis B (three studies); and tetanus–diphtheria–acellular–pertussis (Tdap), meningococcal, HPV, and influenza (three studies) vaccines among adolescents. Health education improves HPV vaccine uptake compared to usual practice (RR 1.43, 95% CI 1.16 to 1.76; I² = 0%; 3 studies, 1054 participants; high-certainty evidence). In addition, one large study provided evidence that a complex multi-component health education intervention probably results in little to no difference in hepatitis B vaccine uptake compared to simplified information leaflets on the vaccine (RR 0.98, 95% CI 0.97 to 0.99; 17,411 participants; moderate-certainty evidence). Financial incentives may improve HPV vaccine uptake compared to usual practice (RR 1.45, 95% CI 1.05 to 1.99; 1 study, 500 participants; low-certainty evidence). However, we are uncertain whether combining health education and financial incentives has an effect on hepatitis B vaccine uptake, compared to usual practice (RR 1.38, 95% CI 0.96 to 2.00; 1 study, 104 participants; very low certainty evidence). Mandatory vaccination probably leads to a large increase in hepatitis B vaccine uptake compared to usual practice (RR 3.92, 95% CI 3.65 to 4.20; 1 study, 6462 participants; moderate-certainty evidence). Provider prompts probably make little or no difference compared to usual practice, on completion of Tdap (OR 1.28, 95% CI 0.59 to 2.80; 2 studies, 3296 participants), meningococcal (OR 1.09, 95% CI 0.67 to 1.79; 2 studies, 3219 participants), HPV (OR 0.99, 95% CI 0.55 to 1.81; 2 studies, 859 participants), and influenza (OR 0.91, 95% CI 0.61 to 1.34; 2 studies, 1439 participants) vaccination schedules (moderate-certainty evidence). Provider education with performance feedback may increase the proportion of adolescents who are offered and accept HPV vaccination by clinicians, compared to usual practice. Compared to adolescents visiting non-participating clinicians (in the usual practice group), the adolescents visiting clinicians in the intervention group were more likely to receive the first dose of HPV during preventive visits (5.7 percentage points increase) and during acute visits (0.7 percentage points for the first and 5.6 percentage points for the second doses of HPV) (227 clinicians and more than 200,000 children; low-certainty evidence). A class-based school vaccination strategy probably leads to slightly higher HPV vaccine uptake than an age-based school vaccination strategy (RR 1.09, 95% CI 1.06 to 1.13; 1 study, 5537 participants; moderate-certainty evidence). A multi-component provider intervention (including an education session, repeated contacts, individualised feedback, and incentives) probably improves uptake of HPV vaccine compared to usual practice (moderate-certainty evidence). A multi-component intervention targeting providers and parents involving social marketing and health education may improve HPV vaccine uptake compared to usual practice (RR 1.41, 95% CI 1.25 to 1.59; 1 study, 25,869 participants; low-certainty evidence). Various strategies have been evaluated to improve adolescent vaccination including health education, financial incentives, mandatory vaccination, and class-based school vaccine delivery. However, most of the evidence is of low to moderate certainty. This implies that while this research provides some indication of the likely effect of these interventions, the likelihood that the effects will be substantially different is high. Therefore, additional research is needed to further enhance adolescent immunisation strategies, especially in low- and middle-income countries where there are limited adolescent vaccination programmes. In addition, it is critical to understand the factors that influence hesitancy, acceptance, and demand for adolescent vaccination in different settings. This is the topic of an ongoing Cochrane qualitative evidence synthesis, which may help to explain why and how some interventions were more effective than others in increasing adolescent HPV vaccination coverage.

Plain-language summary: The review authors found 16 relevant studies. Twelve of the studies were from the USA. The other studies were one each from Australia, Sweden, Tanzania, and the UK. These studies showed the following. When adolescents (girl or boys, or both) and their parents were given vaccination information and education, more adolescents got HPV vaccines (high-certainty evidence). When adolescents were given gift vouchers, more adolescents may have got HPV vaccines (low-quality evidence). However, we were uncertain whether giving adolescents and their parents health education, cash, and gift packages led to more adolescents getting hepatitis B vaccines (very low certainty evidence). When laws were passed stating that adolescents must be vaccinated to go to school, substantially more adolescents probably got hepatitis B vaccines (moderate-certainty evidence). When healthcare providers were reminded to vaccinate adolescents when they opened their electronic medical charts, this probably had little or no effect on the number of adolescents who got tetanus–diphtheria–pertussis, meningococcal, HPV, or influenza vaccines (moderate-certainty evidence). When healthcare providers were given education with performance feedback, more adolescents may have got HPV vaccines (low-certainty evidence). When healthcare providers were given education, individualised feedback, frequent visits, and incentives, more adolescents probably got HPV vaccines (moderate-certainty evidence). When healthcare providers and parents were targeted in several ways, including through education, telephone calls, and radio messages, more adolescents may have got HPV vaccines (low-certainty evidence). These studies compared the use of these approaches (health education, gifts and rewards, laws, or reminders) to using no approaches. In addition, one study from Tanzania gave vaccination information to all girls that were in school class six but were not necessarily of the same age. They were compared to girls who were given vaccination information because they were all born in the same year, but were not necessarily in the same class. This study showed that the class-based approach probably led to slightly more girls getting HPV vaccines (moderate-certainty evidence). How up-to-date is this review? The review authors searched for studies that had been published up to 31 October 2018.