Publication date: Dec 01, 2025

We conducted a randomized, Phase 2 trial to assess the safety and humoral immunogenicity of reduced doses/dose volume of the standard dose of Ad26. COV2. S COVID-19 vaccine (5 cD7 10 viral particles [vp]) in healthy adolescents aged 12-17 years. Participants were randomly assigned to receive Ad26. COV2. S at reduced dose levels of 0. 625 cD7 10 (0. 5 mL), 1. 25 cD7 10 (0. 5 mL) or 2. 5 cD7 10 (0. 5 mL or low volume 0. 25 mL) vp in a 1- or 2-dose (56-day interval) primary schedule. Adolescents who received a 1-dose primary schedule received a 2. 5 cD7 10 vp booster dose 6 months later. Safety and humoral immunogenicity were assessed up to 6 months post-last vaccination. All regimens were well tolerated, with no safety concerns identified. Local and systemic solicited AEs in adolescents were consistent with the known safety profile in adults. All 1- and 2-dose Ad26. COV2. S primary schedules elicited robust peak Spike-binding antibody responses and virus neutralizing titers against the reference strain, in participants with and without preexisting SARS-CoV-2 immunity. Immune responses were durable for at least 6 months. Spike-binding antibody responses were comparable to those elicited in young adults aged 18-25 years who received a standard dose of Ad26. COV2. S in Phase 3 efficacy studies Reduced doses/dose volume of Ad26. COV2. S had an acceptable safety profile and elicited robust humoral immune responses in adolescents aged 12-17 years. All 1- and 2-dose schedules elicited Spike-binding antibody responses that were comparable to an adult population in whom efficacy has been demonstrated using a higher vaccine dose. (clinicaltrials. gov NCT05007080).

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