My main symptom is exercise intolerance, muscle soreness, severe muscle fatigue and feelings of muscle ?heaviness? that can last 3-4 days after even very light exercise. This seems to have started shortly after my last COVID boosters.  I am a 50-year-old woman and I work as a consultant for various humanitarian organizations, most recently in other Countries. In the past I have been in good health, and it has been my habit exercise vigorously. I have participated in half-ironman competitions and have usually exercised 5 or 6 days/week with combinations of running (as far as 10 miles), biking (as far as 50 miles), and swimming (over 1 mile). I enjoyed these activities until December 2021, when my muscle symptoms started.  During the past two years, and especially the last three months, I and my family have had many negative COVID PCR and rapid antigen tests in the course of traveling. I haven't had any of the common symptoms of COVID infection, and I have been very careful to wear NK95 masks and follow appropriate COVID precautions.   In April 2021 while in a Country I received my first dose of Astra Zeneca COVID vaccine. In May after returning, I received 1 PFIZER dose, and in June 2021 a second PFIZER dose. I had mild arm achiness for one or two days after these with some body aches, but I did not have any more general symptoms. (At that time it was not clear whether airlines and border-control agencies would accept doses from 2 different vaccine manufacturers as fulfilling two-dose travel requirements, so I opted to take 2 PFIZER doses after the Astra Zeneca dose.)  On December 13, 2021 I received a COVID booster. This dose was administered at a mass vaccination center and was said to be PFIZER vaccine. However, I could not read PFIZER on the label. A colleague who was vaccinated at the same vaccination center said that when she asked to see the vial used by the health worker, the vial said ?sodium chloride?. Whatever it was, I doubted if the vaccine had been properly refrigerated or if the dose was correct.  After the December 13 booster I had mild arm soreness for a day or two, and around December 20 I developed over 1 or 2 days general muscle soreness and low-grade head and neck aching along with a recurrence of peripheral neuropathy-type symptoms, including tingling and numbness of my arms, legs and face (See previous medical history below). Initially the muscle soreness seemed relieved when I drank 2 liters of an electrolyte and glucose solution over 24 hours. However, during subsequent days my leg muscles became even more sore, especially 8-10 hours after exercise. I sometimes had stabbing pains in my thighs. Because of these symptoms I progressively reduced my exercise from running 9 miles in the hills (late Dec 2021) to walking slowly and for short distances (2-3 miles) on level ground (early Jan 2022). In mid-January I returned to another Country. After 24 hours sitting on a plane and in airports and another 2 days of quarantine at home upon arrival, my symptoms had abated. However, they returned when I engaged in even light activity.  On Jan 13, 2022, because I wasn't sure of the provenance or dosage of the vaccine I had received in December, I elected to take a Moderna booster. This vaccine was delivered by air-freight under proper refrigeration, and was administered at another country. (At that point I had received 1 Astra Zeneca, 2 or 3 PFIZER, and 1 Moderna vaccine.)  On January 14 I participated in a one-hour yoga classes with bodyweight strength training exercises. My muscle strength seemed normal although I was slightly sore afterwards. The following day I attended another yoga class. My muscle strength was normal, but within 15 min after the session, I developed nausea, a feeling of shakiness and an increased heart rate. That night I developed marked muscle soreness, and the muscles in my shoulders, back and legs felt like they were in fire. This was not relieved by Ibuprofen or Celebrex. For several days thereafter I felt like I had run a marathon. At this point my symptoms of peripheral neuropathy also significantly worsened.   The muscle soreness was aggravated by even minimal effort like lifting a backpack, climbing stairs or walking at a slow pace, and was accompanied by a feeling that my limbs were very heavy. Although I was engaging in only light physical activity (no more than 10-20 minutes at a time of slow walking or light household chores), my ability to walk or stand continued to deteriorate over the next 3 days. Standing or slow walking for more than a few minutes caused my legs to shake and gave me mild nausea and dizziness.   I saw an physician who was unsure what was wrong, and on January 20 I returned to see physicians at. The results of their tests have been normal, and no one has been able to come to a diagnosis regarding my muscle symptoms.   Currently, my maximum exercise tolerance is 3-4 miles of slow walking, but even this leaves me very sore. Muscle soreness peaks during the 12-24 hours after even very light exercise (10-20 minutes of walking). At times I also notice a faster heart rate, increased from my usual 50+ to 80-90 even when I am not engaged in any physical activity. I cannot go on walks for 2 or more consecutive days without developing tremors in my thigh muscles. Even very limited strength training (without weights) causes immediate muscle fatigue and weakness, followed by soreness within 6-8 hours. I do not feel tired or need to sleep more than usual.    I have had my CK enzymes checked twice (both during bouts of muscle soreness post physical activity), but the levels have been normal. I have not had a fever, rash, joint symptoms or change in the color of my urine.   Previous medical history Along with my recent muscle symptoms I have also had numbness and tingling. This seems to be a recurrence of symptoms that first occurred and disappeared while I was living in another Country in 2019. At that time I had tingling in my fingers and toes which would wax and wane and last several hours. Over time the episodes involved my hands and feet as well, in a stocking-glove distribution.   In 2019 several hours after strenuous exercise in a hot environment, I had an episode of more intense tingling that involved my distal extremities, face and tongue, and was accompanied by marked nausea. These symptoms lasted about 6 hours and seemed to clear as I drank fluids. During the next 3 to 4 weeks, however, the tingling continued on and off, with fleeting feelings of head pressure or fullness and a metallic taste in my mouth. I had no weakness, fatigue or muscle pain. The symptoms were not precipitated by identifiable factors. I was not worried about anything, or under significant stress.  I consulted a neurologist in the other Country, and his examination and nerve conduction studies on my arms and legs were normal. He discussed the possibility of peripheral neuropathy but did not make a specific diagnosis.    About three months later (December 2019), while visiting, I saw M.D. for neurology consultation. At that time I had been free of symptoms for one or two months and was following my usual exercise routine without trouble. Dr, neuro exam and blood tests were normal. She did not think I had an auto-immune disorder and we discussed the question of small-fiber peripheral neuropathy (SFPN). She thought that a skin biopsy to evaluate this possibility was not warranted.  In mid December 2021 a few days after my PFIZER booster, I began to have along with my muscle symptoms a recurrence of tingling in the same pattern as in 2019. It lasted hours and sometimes was accentuated by exercise, becoming a burning sensation in my feet after running. I developed headaches and momentary electric sensations in my scalp and extremities.   In January 2022 before returning to other Country I had a tele-visit with a neurologist who recommended I have a brain and spine MRI for MS, and blood tests for possible causes of peripheral neuropathy. These tests were normal. In February 2022 a different neurologist raised the question of an auto-immune condition possibly linked to my COVID boosters, but did not recommend any treatment.   At this time my neuropathy type symptoms have largely abated. They flare up to a very limited extent with tingling in my feet and fingertips and face if I engage in physical activity.   My muscle symptoms continue, however, and are disabling. Feelings of muscle fatigue and ?heaviness? can continue 3-4 days after very light exercise.  It is impossible for me to overstate what a huge change this represents in my health and quality of life.