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COVID-19 vaccine side effects, while rare, have been identified in a subset of individuals. The Pfizer and Moderna vaccines played a pivotal role in navigating the global pandemic; however, a small number of people have reported experiencing persistent and debilitating side effects, which they link to these vaccinations.
Initially, many who reported these issues were informed that there was no scientific evidence connecting their conditions to the vaccine, as definitive proof was lacking.
This perspective began to evolve following a February announcement from Yale University researchers, who identified a novel condition termed ‘post-vaccination syndrome’ (PVS).
PVS is characterized by various neurological symptoms including cognitive impairment (brain fog), headaches, and vertigo, alongside other symptoms such as reduced exercise capacity, insomnia, and cardiac inflammation.
Given that several of these symptoms were already prevalent before the pandemic, establishing a direct causal link to the vaccine presents challenges. The complexities of the US healthcare system further complicate diagnostic efforts.
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Dr. Sujana Reddy, a physician specializing in vaccine-related injuries and long COVID, stated to the Daily Mail, ‘Vaccines are overwhelmingly safe and vital for public health. However, it is crucial to acknowledge that a minor segment of the population may face the possibility of enduring symptoms after vaccination.’
‘It is imperative not to disregard these patients. The rarity of an occurrence does not negate its reality.’
The following outlines symptoms that research has associated with COVID-19 vaccines and guidance for individuals experiencing them.
The newly recognized ‘post-vaccination syndrome’ (PVS) may persist for years following administration of mRNA vaccines, such as those developed by Pfizer and Moderna.
A 2024 study identified heart-related conditions like pericarditis and myocarditis as strongly associated with COVID-19 vaccinations.
Neurological Symptoms
Yale University investigators reported that PVS is marked by symptoms such as headaches, vertigo, and cognitive dysfunction, often referred to as ‘brain fog’.
Individuals experiencing these neurological issues may suffer from intense cephalalgia, lightheadedness, weakness or instability, disorientation, cognitive difficulties, impaired concentration, and memory decline.
This cluster of symptoms is commonly observed, typically manifesting within 48 hours post-vaccination, escalating in severity over subsequent days and weeks, and potentially becoming chronic.
A 2022 study conducted by UK researchers documented that headaches, cluster headaches, migraines, and dizziness were the most frequently reported adverse events following administration of the Pfizer and Oxford-AstraZeneca vaccines in the UK.
Among PVS patients evaluated by Yale researchers, cognitive impairment was reported in 78 percent, while 73 percent reported difficulties with concentration or focus.
Separate analysis in 2024 indicated that brain fog was reported in approximately one in 1,000 doses of mRNA COVID-19 vaccines, such as Pfizer’s, and 56 in 1,000 doses of adenoviral vector vaccines, including Johnson & Johnson/Janssen’s.
While headaches are recognized as common vaccine side effects, a 2021 study suggested that post-COVID vaccine headaches could indicate cerebral venous thrombosis, a condition involving potentially fatal blood clots in the brain.
Dr. Zoe Lees, a metabolic medicine specialist, stated to the Daily Mail that experiencing headaches or dizziness post-vaccination is ‘typical’ and generally resolves within a short period.
She elaborated: ‘These symptoms are more likely a consequence of the body’s immune response rather than direct nerve damage. Severe or persistent symptoms are exceptionally uncommon.’
However, Dr. Lees added, ‘If symptoms persist beyond a few weeks, seeking professional medical evaluation is advisable.’
For individuals experiencing headaches or migraines, management may include over-the-counter analgesics or prescription medications, along with lifestyle and dietary adjustments.
Treatments for symptoms such as dizziness, disorientation, and concentration difficulties are highly individualized, often requiring patients to undergo trials of various therapeutic approaches.
Exercise Intolerance
Yale University researchers identified exercise intolerance as a prevalent symptom among PVS patients, affecting 80 percent of the study group.
A 2023 preprint study similarly found that 71 percent of individuals reporting PVS experienced exercise intolerance.
Exercise intolerance is defined by a diminished capacity or difficulty in performing physical activities at a previously comfortable intensity or level of exertion prior to COVID vaccination.
This can manifest as premature breathlessness or excessive fatigue hindering the initiation or completion of physical workouts. Individuals may also experience muscular weakness, discomfort, or pain.
Beyond its association with PVS, exercise intolerance has also been linked to long COVID.
Yale University researchers discovered that in individuals with exercise intolerance, despite normal cardiac and pulmonary function, the body exhibits impaired oxygen extraction and utilization from the bloodstream, which typically fuels physical performance.
Treatment options for exercise intolerance are limited, but medical practitioners may prescribe high-dose vitamins and medications typically used for muscle weakness.
Fatigue and Sleep Disturbances
The 2023 preprint study indicated that excessive fatigue affected 69 percent of individuals reporting PVS, while Yale University researchers reported this symptom in 85 percent of PVS patients.
Furthermore, 70 percent of PVS patients experienced difficulties initiating or maintaining sleep, according to Yale researchers.
The 2022 UK study cited poor sleep quality as one of the most frequently reported side effects following COVID vaccination.
A 2023 study examining the relationship between sleep and COVID vaccines found that individuals who experienced vaccine side effects exhibited reduced sleep duration and quality compared to those without side effects.
Thirteen percent of participants reported moderate to severe insomnia. Nearly four percent experienced difficulty falling asleep; 6.8 percent had trouble staying asleep; and 7.4 percent consistently woke up prematurely.
While cognitive impairment (brain fog) is a symptom of PVS on its own, insufficient or poor sleep can exacerbate it, further impairing concentration and cognitive function. It can also contribute to mood alterations like irritability and depression and elevate the long-term risk of obesity, cardiovascular disease, and diabetes.
Adequate sleep is essential for bodily repair processes and immune system function, fortifying the body’s defenses against viral infections. PVS patients with sleep disturbances may face increased vulnerability to other health complications.
To address sleep problems, clinicians may recommend pharmaceutical interventions, psychotherapy, or modifications to lifestyle and dietary habits.
Dr. Lees informed the Daily Mail that fatigue is also a common side effect of vaccination but typically subsides within one to two weeks.
However, if fatigue persists for more than six weeks, ‘supportive care is available in post-viral syndrome clinics.’
Rory Nairn, a 26-year-old from New Zealand, tragically died from myocarditis 12 days after receiving his first Pfizer COVID vaccine dose in 2021.
Myocarditis
Myocarditis, or inflammation of the heart muscle (myocardium), can compromise the heart’s pumping efficiency, potentially leading to cardiac failure, arrhythmia, and in some instances, sudden cardiac death.
Viral infections are the typical cause of myocarditis, with fewer than 200,000 US cases annually.
Symptoms of myocarditis may include chest discomfort or tightness, dyspnea, fatigue and loss of energy, lower extremity edema, and irregular heart rhythms.
In rare instances, mRNA vaccinations have been associated with myocarditis and pericarditis, the latter being inflammation of the pericardium, the sac surrounding the heart.
The frequency of this side effect remains under investigation. A significant 2021 study in Israel estimated the rate at one in 50,000. Other studies have yielded considerably varying figures.
Dr. Jared Ross, an emergency medicine physician and medical school professor, told the Daily Mail that post-vaccine myocarditis is more prevalent in males, especially those under 30 years of age.
He noted that while typically triggered by viral infections, myocarditis can also be induced by vaccines, most commonly the Moderna COVID vaccine.
CDC data confirms that post-vaccine myocarditis and pericarditis are recognized side effects of COVID vaccination, although the agency does not specify the exact number of cases.
The proposed mechanism is that the immune system might misidentify mRNA components in COVID vaccines as threats, leading to self-attack and subsequent cardiac inflammation.
Both myocarditis and pericarditis have also been associated with COVID-19 itself.
In January 2025, Canadian experts advocated for further research into cardiac complications linked to COVID vaccines.
They emphasized that the true scope of the problem remains ‘under-documented’ due to limitations in study designs, which often fail to assess risks months or years after vaccination.
Researchers from British Columbia also cautioned against inconsistencies in the classification of ‘post-vaccine‘ myocarditis and pericarditis across studies, with varying timeframes used to establish a direct link to vaccination.
Management of myocarditis includes medications, lifestyle modifications, rest, and in severe cases, surgical intervention or cardiac transplantation.
However, Dr. Ross reassured, ‘Fortunately, the majority of patients achieve full recovery.’
Tinnitus, a common auditory condition, typically manifests as a persistent ringing sensation in the ears.
Tinnitus
Tinnitus, an auditory issue frequently characterized by persistent ear ringing, can also present as buzzing, roaring, hissing, or clicking sounds.
Beyond being bothersome and disruptive, tinnitus can cause frequent nocturnal awakenings as the perceived sound intensifies in quiet environments, disrupting regular sleep cycles and potentially leading to insomnia and sleep deprivation.
When these sounds persist for more than six months, it is classified as chronic tinnitus.
A 2024 study published in Frontiers in Pharmacology, analyzing a survey of 398 cases of COVID vaccination-related tinnitus, reported an occurrence of 47 cases per million complete Pfizer COVID vaccine doses.
Tinnitus incidence was also noted at 51 cases per million complete Moderna doses and 70 cases per million for J&J/Janssen doses.
Dr. Hamid Djalilian, chief medical advisor for NeuroMed Tinnitus Clinic, informed the Daily Mail that the Vaccine Adverse Event Reporting System (VAERS) has received approximately 12,000 tinnitus reports following COVID vaccination, ‘but in proportion to the millions of vaccines administered, the overall incidence remains low.’
A team at Stanford Medicine Molecular Neurotology Laboratory is currently investigating the underlying causes of tinnitus and identifying individuals predisposed to developing it after vaccination.
Dr. Konstantina Stankovic, an otolaryngologist-head and neck surgeon leading the research, stated to NBC: ‘We believe that many forms of tinnitus reflect some level of inner ear damage, to which the brain attempts to compensate by generating its own sounds.’
This research is ongoing, and findings are yet to be published.
Typical treatment for tinnitus includes corticosteroids. A case study also reported successful treatment using repetitive transcranial magnetic stimulation (rTMS), a non-invasive brain stimulation technique employing magnetic pulses to modulate brain activity potentially causing ear ringing.
Dr. Djalilian advised that ‘initiating supportive care is paramount’ upon developing tinnitus after vaccination.
He further explained: ‘This includes antioxidants, hydration, and rest. Maintaining composure is essential, as anxiety and stress can exacerbate the condition.’
Kari Ponce de Leon, a 43-year-old mother of two from Montana, reported to the Daily Mail that physicians diagnosed her with multiple blood disorders causing her immune system to impede platelet function.
Blood Clots and Low Platelets
The concurrent occurrence of blood clots and reduced platelet counts following COVID vaccination defines a condition known as thrombosis with thrombocytopenia syndrome (TTS).
The CDC has identified TTS as a rare but serious condition linked to the J&J/Janssen COVID vaccine.
TTS involves the formation of thrombi (blood clots) alongside thrombocytopenia (a decrease in platelet count).
Blood clots migrating through the circulatory system can lead to severe, life-threatening complications such as strokes. Platelets are crucial for blood coagulation and wound healing; insufficient platelets can result in uncontrolled and potentially fatal bleeding.
Symptoms of TTS include severe headaches, blurred vision, speech difficulties, easy bruising, leg pain or swelling, excessive bleeding, and abdominal pain.
A CDC report from August 2021 documented 38 TTS cases within 15 days of COVID vaccination, with four fatalities reported as of July 2021.
At that time, the overall TTS incidence rate was three cases per 1 million doses.
In early 2021, the FDA and CDC recommended a temporary pause on the use of the J&J/Janssen vaccine due to concerns about its association with TTS, after six cases were initially reported.
However, in April 2021, the pause was lifted following a safety review. The agencies concluded that the benefits of the vaccine outweighed the potential risks.
Current data on TTS following COVID vaccination is limited. A 2022 study based on Norwegian data estimated an incidence of five cases per 130,000 individuals.
The researchers inferred a TTS incidence of one case per 26,000 vaccinations.
The precise mechanism by which COVID vaccines induce TTS remains unclear but is believed to be triggered by an aberrant immune response.
Treatment for TTS typically involves anticoagulant medications and infusions of blood products containing specific antibodies.
Kari Ponce de Leon, a 43-year-old mother of two from Montana, disclosed to the Daily Mail that physicians diagnosed her with a series of hematological conditions leading to immune-mediated platelet blockage, mirroring the pathology of TTS.
One physician noted in a letter that her condition was likely attributable to the COVID vaccine ‘as no other etiology could be identified.’
A 2022 study led by researchers at Imperial College London estimated that nearly 20 million lives were saved by COVID vaccines in the first year of global vaccine rollout, predominantly in high-income nations.
Numbness or Burning Sensations
The 2022 UK study identified paresthesia – characterized by tingling, numbness, prickling, or burning sensations throughout the body – as a frequently reported adverse event following Pfizer and Oxford-AstraZeneca vaccination.
In addition, the 2023 preprint study indicated that 63 percent of PVS patients reported numbness, and an equal percentage reported neuropathy, or nerve damage, manifesting as pain, numbness, tingling, or weakness, predominantly in the extremities.
Numbness and burning sensations were also prominent complaints among PVS patients evaluated by Yale researchers.
Eighty percent of patients reported experiencing paresthesia, and 58 percent reported burning sensations.
Management strategies for these symptoms may include over-the-counter analgesics, topical anti-inflammatory agents, off-label use of anxiolytic and anticonvulsant medications, physical and occupational therapy, and lifestyle and dietary adjustments.
Guillain-Barré Syndrome
Dr. Ross explained to the Daily Mail that Guillain-Barré syndrome (GBS) is a neurological disorder where the body’s immune system mistakenly targets and damages its own nerves.
GBS manifests as muscle weakness, numbness, and paralysis.
He stated that GBS is caused by antibodies attacking the nervous system, typically occurring after a viral infection or vaccination, including COVID vaccines.
GBS symptoms encompass unsteady gait, facial movement and speech difficulties, and paresthesia and weakness predominantly in the distal limbs and upper torso. While most patients recover, severe cases can result in paralysis or mortality.
Recent studies have indicated a potential increase in GBS risk among adults aged 18 and older following COVID vaccination.
In the August 2021 CDC report, it was stated that after 12.6 million doses of the J&J/Janssen vaccine administered, 100 GBS reports were received between February and June of that year.
At that time, the GBS incidence rate was approximately eight cases per million J&J/Janssen vaccine doses.
A separate 2023 study published in The Cureus Journal of Medical Science suggested that vector-based COVID vaccines, such as the J&J/Janssen vaccine, could more than double an individual’s likelihood of developing GBS.
Vector vaccines utilize a harmless virus to transport genetic material into the body, triggering an immune response against the targeted disease.
Researchers conducting a review of 70 studies on post-vaccination GBS found that 80 percent of affected patients developed GBS within 21 days after the first dose of a vector vaccine.
Dr. Lees mentioned to this website that a meta-analysis estimated the overall GBS incidence to be four per 1 million doses of adenovirus vector vaccines.
However, Dr. Lees, a medical writer at ZipHealth, clarified that a COVID-19 infection itself is associated with an elevated GBS risk – ‘higher than any potential risk linked to vaccination.’
While the precise mechanism for vaccine-triggered GBS remains under investigation, it was noted that most affected patients were successfully treated, with a single fatality reported due to autonomic dysfunction – a condition impairing involuntary bodily functions.
There is no definitive cure for GBS. Treatment focuses on symptomatic relief and preventing complications through interventions such as blood purification, respiratory support, and physical rehabilitation.