ACUTE KIDNEY INJURY SECONDARY TO TACROLIMUS TOXICITY; SUSPECTED CLINICAL VACCINATION FAILURE; SUSPECTED COVID-19 INFECTION; This spontaneous report received from a pharmacist via other manufacturer Pfizer concerned a male of unspecified age. Initial information was processed with the additional information received on 09-JUN-2022. The patient's height, and weight were not reported. The patient's past medical history included: kidney transplant on 02-SEP-2020 and concurrent conditions included: gout, hyperlipidemia, and hypertension. The patient received covid-19 vaccine ad26.cov2.s (dose number in series 1) (suspension for injection, route of administration, batch number and expiry were not reported) dose was not reported, 1 total, administered on 10-MAR-2021 for prophylactic vaccination. The batch number was not reported and has been requested. The patient received two doses of non-company suspect vaccine included: Moderna covid 19 vaccine (elasomeran) (dose number in series 2) (form of administration and route of administration were not reported, batch number: unknown, expiry: unknown) dose was not reported, dose 1 administered on 28-OCT-2021 and dose 2 administered on 18-MAR-2022 for prophylactic vaccination.  Non-company suspect drugs included: tacrolimus (form of admin unknown, oral, batch number was not reported, expiry: unknown) dose and frequency were not reported from an unspecified date to 19-MAY-2022 for an unspecified indication. Concomitant medications included carvedilol, allopurinol, colecalciferol, fenofibrate, fish oil, mycophenolate mofetil, Acetaminophen (paracetamol), prednisone, semaglutide, and multivitamin for unknown indication.  On 10-MAY-2022, patient felt nauseous and weak (dose number in series 2) and was instructed to go to the emergency room (ER). Serum creatinine on admit to the emergency department (ED) was 2.25 g/dl (baseline of 1.5 to 1.8 g/dl). Tacrolimus level was not drawn. Patient was discharged home from the ED with instruct to hold tacrolimus. On 17-MAY-2022, home covid-19 virus test was positive. Thus patient experienced suspected covid-19 infection (dose number in series 2) and suspected clinical vaccination failure (dose number in series 1). The patient was prescribed with Paxlovid (Nirmatrelvir/Ritonavir) 300/100, twice a day for 5 days during 17-MAY-2022 to 21-MAY-2022 for covid-19 treatment. During emergency room (ER), interaction between the paxlovid and tacrolimus was identified. Patient was told to hold his simvastatin and tamsulosin. On 21-MAY-2022, Laboratory data included: Tacrolimus level (NR: not provided) 75.6 ng/mL, and Serum creatinine (NR: not provided) 2.59 g/dL. On 21-MAY-2022, patient was admitted for acute kidney injury (AKI) secondary to tacrolimus toxicity, for which he started on fluids and given 2 doses of phenytoin 300 milligram (dose number in series 2). Patient was hospitalized for 2 days. On 23-MAY-2022, patient was discharged from the hospital with serum creatinine 2.48. Patient was instructed to hold on tacrolimus, simvastatin, tamsulosin at discharge. The action taken with covid-19 vaccine ad26.cov2.s, and elasomeran was not applicable; and treatment with tacrolimus was withdrawn on 19-MAY-2022. The patient recovered from suspected covid-19 infection on MAY-2022, and the outcome of suspected clinical vaccination failure and acute kidney injury secondary to tacrolimus toxicity was not reported. This report was serious (Hospitalization Caused / Prolonged). This report was associated with product quality complaint: 90000234819.; Sender's Comments: V0- 20220610670-Covid-19 vaccine ad26.cov2.s- Acute kidney injury, Suspected Covid-19 infection. The event(s) shows an incompatible temporal relationship. Therefore, this event(s) is considered not related. 20220610670-Covid-19 vaccine ad26.cov2.s-Suspected clinical vaccination failure. The event(s) has a compatible/suggestive 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: SPECIAL SITUATIONS. Therefore, this event(s) is considered not related.