NON-OCCLUSIVE SUPERFICIAL THROMBOSIS OF GREATER SAPHENOUS VEIN; OFF LABEL USE IN UNAPPROVED ROUTE OF ADMINISTRATION; This spontaneous report was received from physician via literature: This report concerned a 64 year old African American female of an unspecified ethnicity. The objective of the study is to discuss a case of VTE (venous thromboembolism) occurring shortly after Janssen COVID-19 vaccine administration and to highlight characteristics of this complication and discuss pertinent changes in patient management when there is concern for adenovirus-vector vaccine-associated VTE. The patient's height, and weight were not reported. The patient's past medical history included: symptomatic menorrhagia due to uterine fibroids, and concurrent conditions included: hypertension, and hyperlipidemia, and smoker (5 pack year history greater than 20 years prior), and other pre-existing medical conditions included: The patient did not have a personal or family history of thrombotic or hemorrhagic disorders, including venous thromboembolism. The patient denied trauma to the right lower extremity, recent travel, infection (including COVID-19), surgical procedures, or periods of prolonged immobility in the past year. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, subcutaneous, batch number was not reported) dose was not reported, 1 total administered on 06-APR-2021 for covid-19 prophylaxis. The batch number was not reported and has been requested. Age at the time of vaccination 7 decades old. No concomitant medications were reported.  On 06-APR-2021, the patient received a single dose of the Janssen covid-19 vaccine subcutaneously which was an off label use in unapproved route of administration (Off label use), without an immediate adverse reaction.  On 12-APR-2021, six days later a family member noted a small ecchymosis on her medial left calf, which prompted the patient to present to a local emergency department on 14-APR-2021. On arrival, she was hemodynamically stable without fever, hypotension, or tachycardia. Her Body mass index (BMI) was 30 and 5 pack year history greater than 20 years prior. She ambulated independently and was up to date with her age appropriate malignancy screenings, all of which were negative. A physical exam in the emergency department revealed unilateral 2 plus pitting edema of the right lower extremity below the right knee and a small ecchymosis on her medial left calf without associated erythema, paresthesia, pain, or sensitivity to touch. The flu/SARS-CoV-2 real-time PCR assay was negative for COVID-19. Complete blood count (CBC) showed a WBC (white blood count) count of 6.9 k/uL (reference range: 4.5-11 k/uL), hemoglobin of 13 gm/dL (reference range: 11.2-14.7 gm/dL), hematocrit 39.8% (reference range: 36.0-45.0%), and platelet count of 276 k/uL (reference range 150-400 k/uL). A basic coagulation profile revealed a mildly elevated PT (Prothrombin Time) of 13.8 seconds (reference range: 9.4-13.5) with INR of 1.1 (reference range: 0.8-1.1) and partial thromboplastin time (PTT) of 33.5 seconds (reference range: 24.7-36.3 seconds). Liver function tests were within normal limits except for a mild elevation in alkaline phosphatase of 137 (reference range: 38-126 U/L). D-dimer was elevated to 772 ng/mL (DDU) (reference range: 0-243 ng/mL (DDU)) and anti-heparin (PF4) IgG antibodies had a normal optical density of 0.107 (reference range: 0.00 - 0.4 optical density). Fibrinogen result was not reported. More extensive hypercoagulable workup, anti-phospholipid antibody studies, and factor deficiencies were initially not performed given this was her first DVT. Left lower extremity duplex ultrasound revealed a non-occlusive superficial thrombosis in the greater saphenous vein at the level of the mid-calf. The patient received one dose of apixaban and shortly afterward was unable to speak due to a locked jaw and back arching. She was transitioned to warfarin and developed similar symptoms six days later. Neurology evaluated the patient and deemed the presentation most consistent with psychogenic non-epileptiform seizures given CT head and electroencephalogram were normal. Warfarin was discontinued and replaced with fondaparinux, which the patient continued without incidence or adverse effects until 25-MAR-2022, when her outpatient hematologist repeated a lower extremity duplex, which was negative for any deep or superficial venous thrombosis. During this period the patient had no other documented medical incidents which may have been adverse events secondary to vaccination, such as Bell's palsy, Guillan Barre Syndrome, cerebrovascular accidents, or myocardial infarcts. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from non-occlusive superficial thrombosis of greater saphenous vein, and the outcome of off label use in unapproved route of administration was not reported. The authors concluded it is possible that VTE may be an adverse effect of the Janssen vaccine or any adenovirus-based vaccine but further surveillance and investigation to elucidate this association is necessary. As this information is crucial to provide anticipatory guidance to patients. Until there is further knowledge of VTE risk after adenovirus-based vaccine administration, they suggest an early ultrasound duplex to evaluate for VTE and avoiding heparin products in patients with clinical symptoms concerning for VTE following adenovirus-based COVID-19 vaccination. This report was serious (Other Medically Important Condition). This case, from the same reporter is linked to 20210514897.; Sender's Comments: V0: 20230712936- non-occlusive superficial thrombosis of greater saphenous vein. The event has a compatible/suggestive temporal relationship, and is labeled. There are other factors more likely to be associated with the event. Specifically: MEDICAL HISTORY. Therefore, this event is considered inconsistent with vaccine administration.