This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP). Other Case identifier(s): 2021CAT00100. A 60-year-old female patient received BNT162b2 (BNT162B2), on 08Mar2021 at 16:00 as dose number unknown, single (Batch/Lot number: unknown) at the age of 60 years for Covid-19 immunisation; amifampridine phosphate (FIRDAPSE), first regimen since 09Apr2019 (Lot number: 3185425, Expiration Date: 28Feb2022) at 20 mg 4x/day and second regimen (ongoing) (Lot number: 3190272, Expiration Date: 31Mar2024) at 20 mg 4x/day, all oral for myasthenic syndrome. The patient's relevant medical history included: "Muscular weakness" (unspecified if ongoing); "Hypertension" (unspecified if ongoing); "Myasthenic Reaction", start date: 2011 (unspecified if ongoing), notes: Since 2011; also reported as "for 16 years" relative to 13Apr2022. Concomitant medication(s) included: PYRIDOSTIGMINE. Past drug history included: 3-4 dap for Myasthenic Reaction, notes: Reaction: No adverse event. Vaccination history included: Ruzurgi (Drug Reaction: No adverse event), for Myasthenic Reaction. The following information was reported: MUSCULAR WEAKNESS (medically significant) with onset 08Mar2021, outcome "unknown", described as "More muscle weakness"; FALL (medically significant) with onset 09Mar2021, outcome "unknown", described as "Fell at 4 AM and 8 AM on Tuesday (09-MAR-2021) and at an unspecified time on Wednesday morning"; LIGAMENT SPRAIN (medically significant) with onset 10Mar2021, outcome "not recovered", described as ""Twisted" or "sprained" her ankle". The event ""twisted" or "sprained" her ankle" required physician office visit. The patient underwent the following laboratory tests and procedures: X-ray: (10Mar2021) Results not reported, notes: Results not reported; they sent her to a foot doctor. The action taken for amifampridine phosphate was unknown. Therapeutic measures were taken as a result of ligament sprain. Clinical information: The patient started treatment with FIRDAPSE 10 MG at 20 mg, taken orally, 4x/day, for LEMS. On 08Mar2021, the patient received the COVID-19 Vaccine (Pfizer) at an unreported dose and route of administration, once at 4 PM, for an unreported indication. On 08Mar2021, after starting the products, the patient experienced more muscle weakness. On 09Mar2021, the patient fell at 4:00 AM and 8:00 AM. In the morning on 10Mar2021, the patient fell again, and she twisted her ankle (also reported as "sprained her ankle"). She went to the doctor and sought medical attention. She had an x-ray (results not reported). The patient was given a boot to wear on her ankle for 4 weeks as treatment. The reporter felt it was unlikely the patient broke her ankle, as she was wearing a boot. Additionally, the reporter queried whether there were any interactions between the FIRDAPSE and the Pfizer COVID-19 Vaccine. As of 11Mar2021, treatment with FIRDAPSE was ongoing, and the status of further treatment with the COVID-19 vaccine was not reported. The patient's sprained ankle was not resolved, and the statuses of the muscle weakness and falls were not reported. No additional information was provided. On 30Mar2021, it was learned that the patient's medical history included LEMS since 2011 and high blood pressure. Concomitant products included pyridostigmine 60 mg, 5-6 times; pyridostigmine 180 mg, 1x/day; and unspecified high blood pressure medications. In the evening of 08Mar2021, the patient had her shot (presumed COVID-19 Vaccine). On 09Mar2021, around 04:00, the patient fell and didn't injure anything. At a subsequent unspecified time, she had another fall where she didn't injure anything. On the morning of 10Mar2021, she fell in the kitchen and sprained her ankle. The patient went to acute care and had an x-ray performed, and they sent her to a foot doctor. Her foot was placed into a boot. It was believed that the muscle weakness and falls were all related and may have had something to do with her COVID Vaccine. As of 30Mar2021, the patient's muscle weakness and twisted/sprained ankle were improved, and she had no more falls since 10Mar2021. No additional information was provided. On 13Apr2022, it was learned that the patient had LEMS for 16 years (previously reported as since 2011). The patient's medical history was updated to include past use of 3-4 DAP (diaminopyridine; compassionate use program) and then Ruzurgi (amifampridine) for LEMS prior to FIRDAPSE. It was reported that the patient started treatment with FIRDAPSE on 09Apr2019 (initially reported as 12Feb2019). On an unspecified date, "for years" (relative to 13Apr2022), but not specified if before or after initiating treatment with FIRDAPSE, the patient experienced double vision. The patient felt the double vision was due to LEMS and her physician was aware. As of 13Apr2022, treatment with FIRDAPSE and the double vision were ongoing. No additional information was provided. The information on the batch/lot number for BNT162b2 has been requested and will be submitted if and when received.