ACUTE FEMORAL-TO-PERONEAL DVT IN THE RIGHT LEG AND A CHRONIC FEMORAL DVT IN THE LEFT LEG; This spontaneous report was received from literature: THE CLOT THICKENS: DOES THE JOHNSON & JOHNSON COVID-19 VACCINE INCREASE THE RISK OF THROMBUS IN A HYPERCOAGULABLE STATE?. CHEST 2021. 2021 Oct 11; 160/4. This report concerned a 54-year-old female of an unspecified ethnic origin. The patient's height, and weight were not reported. The patient's past medical history included: severe covid-19 infection, and concurrent conditions included: antiphospholipid syndrome (APS). Prior APS panel for lupus anticoagulant antibody (Ab) on initial and repeat testing was positive. Anticardiolipin and beta-2 glycoprotein Ab were negative. Her complication from APS included chronic left lower extremity deep vein thrombosis (DVT) since 2018. She was compliant with warfarin. The patient received Covid-19 vaccine ad26.cov2.s (suspension for injection, route of administration, batch number; unknown, and expiry date: unknown) dose was not reported, frequency time was 01 total, start therapy date was not reported (twenty days prior to present visit) for prophylactic vaccination. The batch number was not reported and has been requested.  Concomitant medications included warfarin for chronic left lower extremity DVT.  On an unspecified date, fifteen days after receiving the vaccine, she developed bilateral lower extremity swelling and calf pain, left worse than right. On exam, vital signs were within normal limits. She had 1 plus non-pitting edema and tenderness in her left calf, worse compared to the right. Complete blood count showed platelets 172 10 rest to 9/L (reference range: 167-378 10 rest to 9/L). international normalized ratio (INR) 3.03, prothrombin time 33 seconds (reference range: 9.8-12.9). COVID-19 Immunoglobulin G (IgG) titer 8.08 index (S/C) (reference range: 0 - 1.39). Heparin-induced thrombocytopenia (HIT) screen was negative. Venous Doppler ultrasound showed an acute femoral-to-peroneal DVT in the right leg and a chronic femoral DVT in the left leg. Due to recent joint statement by the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) advising against heparin in patients with new thrombi after receiving the J&J vaccine due to HIT-like behavior of these thrombi, the patient was treated with rivaroxaban and was currently doing well. The action taken with Covid-19 vaccine ad26.cov2.s was not applicable. The patient was recovering from acute femoral-to-peroneal DVT in the right leg and a chronic femoral DVT in the left leg. Author emphasized on the correlation, that had been shown between severity of COVID-19 and degree of inflammation. Severe illness leads to generation of excessive inflammatory cytokines and chemokines, endothelial dysfunction, and a host of other pathways to increase risk of thrombosis. This report was serious (Other Medically Important Condition).; Sender's Comments: V0: 20211023622-COVID-19 VACCINE AD26.COV2.S-acute femoral-to-peroneal DVT in the right leg and a chronic femoral DVT in the left leg.. This event(s) is considered not related. 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: UNDERLYING DISEASE