4/34 aSOTRs experienced breakthrough infection between 3-6 months post D3; 4/34 aSOTRs experienced breakthrough infection between 3-6 months post D3; This is a literature report.  An adolescent patient received bnt162b2 (BNT162B2), as dose 1, single (Batch/Lot number: unknown), as dose 2, single (Batch/Lot number: unknown) and as dose 3 (booster), single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history included: "Adolescent solid organ transplant recipients" (unspecified if ongoing). The patient's concomitant medications were not reported. The following information was reported: DRUG INEFFECTIVE (medically significant), COVID-19 (medically significant), outcome "unknown" and all described as "4/34 aSOTRs experienced breakthrough infection between 3-6 months post D3".   Purpose: Adolescent solid organ transplant recipients (aSOTRs) who receive three doses of SARS-CoV-2 mRNA vaccine experience high seroconversion rates and antibody persistence for up to 3 months. Long-term antibody durability beyond this timeframe remains unknown. We describe antibody responses 6 months after third vaccine dose (D3) of the BNT162b2 mRNA vaccine among aSOTRs. Methods: Participants in a multi-center, observational cohort who received thethird 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.Results: In this observational cohort, 34/34 (100%) participants had positive antibody titers 6 months post-D3 (Figure 1) with a median (IQR) of 2500 U/mL (1927-2500).8/34 (24%) aSOTRs had decreased titers at 6 months compared to 3 months (mean decrease of 617 U/mL) and 2/34 (6%) had increased titers (mean increase of 312U/mL). The remaining 24/34 (70%) aSOTRs had stable titers of >2500 U/mL from3 to 6 months post D3. A total of 4/34 aSOTRs experienced breakthrough infection between 3-6 months post D3, all of whom had antibody titers of >2500 U/mL at both3- and 6-month time intervals. 4/34 (12%) aSOTRs reported infection 6-12 months post-D3. Mean 6 month antibody titers (U/mL) were 927 among those infected6-12 months post-D3 (n=4) vs. 2174 among those not infected post D3 (n=26).At 3 months, mean antibody levels (U/mL) were 1275 among those infected 6-12months post-D3 (n=4) vs 2345 (n=26) among participants not infected post-D3.Conclusions: In this observational cohort, antibody titers remained positive 6months following D3, indicating antibody durability among aSOTRs. Antibody titers remained stable after receipt of D3, with only a small subset of participants experiencing a decrease in titers compared to their 3-month post-D3 levels. Lower antibody titers at both 3 and 6 months post-D3 may be associated with increased risk of breakthrough infection >6 months post D3.; Sender's Comments: Based on the information currently available, a lack of efficacy with bnt162b2 vaccine in this patient cannot be completely excluded.   ,Linked Report(s) : US-PFIZER INC-PV202300181666 Same article/ drug/event and different patient;US-PFIZER INC-202300356427 Same article/ drug/event and different patient;US-PFIZER INC-202300356426 Same article/ drug/event and different patient;US-PFIZER INC-202300356422 Same article/ drug/event and different patient;US-PFIZER INC-202300356423 Same article/ drug/event and different patient;US-PFIZER INC-202300356425 Same article/ drug/event and different patient;