AbstractBackgroundAdolescent solid organ transplant recipients (aSOTRs) who received three doses of the COVID‐19 mRNA vaccine experience high seroconversion rates and antibody persistence for up to 3 months. Long‐term antibody durability beyond this timeframe following three doses of the SARS‐CoV‐2 mRNA vaccine remains unknown. We describe antibody responses 6 months following the third vaccine dose (D3) of the BNT162b2 mRNA vaccination among aSOTRs.MethodsParticipants in a multi‐center, observational cohort who received the third dose of the vaccine were analyzed for antibodies to the SARS‐CoV‐2 spike protein receptor‐binding domain (Roche Elecsys anti‐SARS‐CoV‐2‐S positive: ≥0.8, maximum: >2500 U/mL). Samples were collected at 1‐, 3‐, and 6‐months post‐D3. Participants were surveyed at each timepoint and at 12‐months post‐D3.ResultsAll 34 participants had positive anti‐RBD antibody titers 6 months post‐D3. Variations in titers occurred between 3 and 6 months post‐D3, with 8/28 (29%) having decreased antibody levels at 6 months compared to 3 months and 2/28 (7%) reporting increased titers at 6 months. The remaining 18/28 (64%) had unchanged antibody titers compared to 3‐month post‐D3 levels. A total of 4/34 (12%) reported breakthrough infection within 6 months and 3/32 (9%) reported infection after 6–12 months following the third dose of the SARS‐CoV‐2 mRNA vaccine.ConclusionsThe results suggest that antibody durability persists up to 6 months following three doses of the SARS‐CoV‐2 mRNA in aSOTRs. Demography and transplant characteristics did not differ for those who experienced antibody weaning. Breakthrough infections did occur, reflecting immune‐evasive nature of novel variants such as Omicron.