Background: Fear of needles is distressing but can also lead to avoidance of vaccinations, blood donation, and medical tests and treatments. Working with adolescents with needle fears, we developed an automated virtual reality (VR) therapy. We set out to evaluate its efficacy. Methods: We conducted an initial proof-of-concept cohort study followed by a Phase II randomised controlled trial. Participants were included if they were 12-15 years old and had significant needle fears that they would like treated. The proof-of-concept testing was a pre- to post- cohort study. To proceed to an RCT an effect size of at least 0.6 on the Injection Phobia Scale – Anxiety (child version) (IPS) was required. The Phase II test was a parallel group, single-blind, randomised controlled trial in one centre in England. Participants were randomly assigned (1:1) to either the VR therapy or no treatment, using a permuted blocks algorithm with randomly varying block size. The VR therapy was provided in approximately three sessions over two to three weeks. The trial assessor was masked to group allocation. Outcomes were assessed at 0, 3 (end of treatment) (primary endpoint), and 6 weeks. The primary outcome was needle fear, assessed by the IPS. Outcome analyses were done in the intention-totreat population. Moderation and mediation tests were also planned. The RCT was prospectively registered with the ISRCTN registry, ISRCTN74002253. Findings: From March 26th, 2024, to June 7th, 2024, 12 participants (5 [42%] males; 6 [50%] females, 1 [8%] prefer not to say, mean age 13.4 years [SD=0.8, range 12–15]; 10 [83%] White, 1 [8%] other, 1 [8%] prefer not to say) were recruited for the cohort study. After the VR therapy, needle fears as assessed by the IPS reduced on average by 15.2 points [95% C.I. 9.2, 21.1, n=11, Cohen’s d=1.5]. There were no serious adverse events. The RCT could therefore proceed. From October 28th, 2024, to July 15th, 2025, 60 participants (26 [43%] males; 32 [53%] females, 2 other [3%], mean age 13.4 years [SD=0.9, range 12- 15]; 57 [95%] White, 3 [5%] other) were recruited for the RCT. Compared with no treatment, there was strong evidence that VR therapy led to a reduction in needle fears (adjusted mean difference=-14.07, 95% C.I. -17.40, -10.73, p<.001, n=60, Cohen’s d=1.34). The benefits were maintained at follow-up (adjusted mean difference=-14.67, 95% C.I. -18.00, -11.33, p<.001, n=60, Cohen’s d=1.39). There were no serious adverse events. Interpretation: An automated VR therapy, which is potentially scalable, had efficacy in reducing selfreported needle fears in adolescents. Given that this is an age at which people often have a formative experience of medical procedures, it is an important time to reduce needle fears. The intervention requires testing in a Phase III clinical trial. A key focus would be assessing whether the VR therapy increases vaccine uptake in young people who have initially refused due to needle fears. Funding: Beryl Alexander Charity and the NIHR Oxford Health Biomedical Research Centre and NIHR Oxford Biomedical Research Centre.