SUSPECTED IMMUNOLOGICAL VACCINE FAILURE; This spontaneous report was received from literature. This report concerned a 30 year old female. The objective of this article was to study immunogenicity of Ad26.COV2.S Prime and Two Subsequent doses of mRNA SARS-CoV-2 vaccines in solid organ transplant recipients. The patient's height, and weight were not reported. The patient's past medical history included: kidney transplant (5 years since transplant.), and other pre-existing medical conditions included: The patient was immunocompromised. The patient did not had covid-19 prior to vaccine. The patient received covid-19 vaccine ad26.cov2.s (Dose number in series 1) (suspension for injection, route of admin, and batch number were not reported) dose was not reported, 1 total, start therapy date were not reported for covid-19 prophylaxis. The duration between dose 1 and dose 2 was 69 days. The batch number was not reported and has been requested. Concomitant medications included mycophenolate mofetil, and tacrolimus. On an unspecified date, the patient experienced suspected immunological vaccine failure (Dose number in series 1). The patient did not report any breakthrough infection. Laboratory data (dates unspecified) included: Anti RBD (anti-receptor binding domain, negative less than 0.8 U/mL) 0.4 R (Highest Post-D1 Titers). It was reported that, the highest antibody results collected after doses 2 (D2) and 3 (D3) on the Roche Elecsys Anti-SARS-CoV-2 enzyme immunoassay (EIA) (anti receptor binding domain [RBD], negative less than 0.8 U/ml) or (E) EUROIMMUN EIA (anti-S1, negative less than 1.1 AU) were compared. High-positive (anti-RBD more than or equal to 250 U/ml or anti-S1 more than or equal to 4 AU) levels were defined according to reported association with neutralization of wild-type virus. The patient received two doses of (Pfizer covid-19 vaccine) tozinameran (Dose number in series 2) (form of admin, route of admin, and batch number were not reported) dose was not reported, start therapy dates were not reported for covid-19 prophylaxis. Days between dose 2 and dose 3 were 21. Days between D3 and post-D3 titers was 27 days.Lab data: Highest Post-D2 Titers were 0.1 E (EUROIMMUN anti-S1 EIA (units: AU)) and post Dose 3 were less than 0.8 R (Roche anti-RBD EIA (units: U/mL). It was unknown whether patient had any adverse events following vaccination with two doses of Pfizer covid-19 vaccine (Dose number in series 2). The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of suspected immunological vaccine failure was not reported. The authors emphasized on the awareness that despite suboptimal antibody response to the Ad26.COV2.S prime, two subsequent mRNA 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.  This report was serious (Other Medically Important Condition). This case, from Same Literature article is linked to 20221034755, 20221034707, 20221034625, 20221034742, 20221012832 and 20221034752. This report was associated with product quality complaint.; Sender's Comments: V0: 20221034754-covid-19 vaccine ad26.cov2.s-suspected immunological vaccine 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.