SUSPECTED IMMUNOLOGICAL VACCINATION FAILURE; This spontaneous report was received from literature. This report concerned a 40 year old female of an unspecified race and ethnic origin. The patient's height, and weight were not reported. The patient's past medical history included: kidney transplant (8 years since the transplant). The objective of this article was to study. The patient received covid-19 vaccine ad26.cov2.s (Dose number in series 1) (suspension for injection, route of admin not reported, batch number: unknown, expiry: unknown) dose not reported, 01 total administered on an unspecified date for covid-19 prophylaxis. The batch number was not reported and has been requested. Concomitant medications included Mycophenolic acid (MPA), tacrolimus and steroid for an unspecified indication. On an unspecified date laboratory test included: Antibody test (anti-RBD) which was less than 0.8 U/mL ((R: Roche anti-RBD EIA) (units: U/mL) (Highest Post-D1 (ad26.cov2.s) Titers), 47 U/mL ((R: Roche anti-RBD EIA) (units: U/mL) (Highest Post-D2 (tozinameran) Titers), 531 U/mL ((R: Roche anti-RBD EIA) (units: U/mL) (Highest Post-D3 (tozinameran) Titers). The reported range of negative sero-response cut-off was anti-RBD less than 0.8 U/mL or anti-S1 less than 1.1 AU which resulted to suspected immunological vaccine failure (Dose number in series 1). Days between D3 and Post-D3 titers was 29 days and Days between D1 and Post-D2 titers was 95 days, while Days between D2-D3 was 24 days. The patient additionally received two doses of non-company suspect vaccine (Pfizer) (BNT162b2 tozinameran) (Dose number in series 2) (form of admin and route of admin were not reported, batch number: unknown, expiry: UNKNOWN) dose was not reported, administered on an unspecified date for covid-19 prophylaxis (Dose number in series 2). The vaccination days in between ad26.cov2.s and tozinameran was 95 days while vaccination days in between first dose of tozinameran and second dose of tozinameran was 24 days. It was unknown whether the patient experienced any adverse events following vaccination with both the doses of tozinameran(Dose number in series 2). The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of suspected immunological vaccination failure was not reported. The authors emphasized on the awareness that despite suboptimal antibody response to the Ad26.COV2.S prime, two subsequent mRNA SARS-CoV-2 (BNT162b2) vaccines increased antibody titers to high levels for the majority of participants, with acceptable side effects. This series suggested that a heterologous vaccine regimen may be a reasonable option for SOTRs (Solid Organ Transplant Recipients) though lack of sero-response, despite two mRNA boosters, suggested that some recipients may remain at risk for SARS-CoV-2 infection. Comparison of the humoral and cellular responses to three-dose heterologous versus homologous vaccination was needed. This report was serious (Other Medically Important Condition). This case, from the same reporter is linked to 20221034707, 20221034755, 20221034754 and 20221012832 and 20221034742. This report was associated with product quality complaint.; Sender's Comments: V0: 20221034625-covid-19 vaccine ad26.cov2.s-suspected immunological vaccination failure. The event(s) has an unknown/unclear temporal relationship, is unlabeled, and has unknown scientific plausibility. There are other factors more likely to be associated with the event(s) than the drug. Specifically: CONMEDS-OTHER SUSPECT DRUGS, SPECIAL SITUATIONS. Therefore, this event(s) is considered not related.