The Covid vaccines made by Pfizer and Moderna helped lift the world out of the pandemic, but a small group of people were left with debilitating side effects that they attribute to the vaccine.
Many were told there was no evidence the shot caused it — because there wasn’t.
The situation changed slightly in February when a team from Yale University said they had discovered a new condition known as ‘post-vaccination syndrome’ (PVS).
The syndrome appeared to cause neurological issues such as brain fog, headaches and dizziness, and many other symptoms including exercise intolerance, insomnia and inflammation of the heart.
Many of these symptoms were commonly reported before the pandemic, so there is no easy way to prove if they are actually caused by the vaccine or are unrelated, and the fragmented US health care system complicates the picture further.
Dr Sujana Reddy, a physician specializing in vaccine-associated injury and long Covid, told the Daily Mail: ‘For the vast majority of people, vaccines are safe and lifesaving. But we do need to acknowledge that, in a small subset of individuals… there may be a risk of persistent symptoms post-vaccination.
‘These patients shouldn’t be dismissed. Just because something is rare doesn’t mean it’s not real.’
Below, the Daily Mail reveals the symptoms research has linked to vaccines and what to do if you experience them.
The previously-unknown condition, dubbed ‘post-vaccination syndrome’ (PVS), can persist years after taking the mRNA vaccines— made by the likes of Pfizer and Moderna
A 2024 study looked at the conditions most associated with Covid vaccinations. Heart issues like pericarditis and myocarditis were most often linked to the shots
Neurological symptoms
The Yale researchers reported that PVS is characterized by symptoms such as headaches, dizziness and ‘brain fog’.
People who experience these symptoms may suffer from debilitating head pain, feeling faint, weak or unsteady, confusion, thinking difficulty, problems with concentration and diminishing memory.
This group of symptoms are among the most common and usually develop within 48 hours of receiving a vaccine and become more severe in the following days and weeks, and can persist over time.
A 2022 study by UK researchers found the most frequently reported adverse events after receiving the Pfizer and Oxford-AstraZeneca in the UK were headaches, cluster headaches, migraines and dizziness.
Among the PVS patients analyzed by the Yale researchers, brain fog was reported in 78 percent of people and difficulty concentrating or focusing was reported by 73 percent.
A separate 2024 analysis found brain fog was reported in about one in 1,000 doses of an mRNA Covid vaccine – such as Pfizer’s – and 56 in 1,000 doses of an adenoviral vector vaccine – such as Johnson & Johnson/Janssen’s.
And while headaches can be common side effects of vaccines, a 2021 study found headaches post Covid vaccine could be a sign of cerebral venous thrombosis – deadly blood clots that form in the brain.
Dr Zoe Lees, who studies metabolic medicine, told the Daily Mail that it is ‘common’ to have headaches or dizziness after a vaccine but they typically resolve in a short timeframe.
She said: These symptoms are more likely to be due to the body’s immune response rather than direct damage to nerves. Severe or frequent symptoms are extremely rare’
However, she added: ‘If symptoms [last] more than a few weeks, it is appropriate to seek further evaluation.’
For people experiencing headaches or migraines, treatment can include over-the-counter pain medication or prescription drugs, as well as lifestyle and diet changes.
Treatments for symptoms like dizziness, confusion and difficulty concentrating can vary widely based on the individual and people typically have to trial and error multiple therapies.
Exercise intolerance
Yale researchers found exercise intolerance was among the most commonly reported symptom of people with PVS — with 80 percent of people suffering from it.
And a 2023 preprint paper found exercise intolerance was suffered by 71 percent of people reporting PVS.
Exercise intolerance is characterized by the inability or struggle to perform physical activity at a person’s desired intensity or at the same caliber they exercised at prior to receiving a Covid vaccine.
This may manifest as running out of breath sooner than usual or being too tired to start or complete a work out. People may also experience muscle weakness, aches or pain.
In addition to being linked to PVS, exercise intolerance has also been associated with long Covid.
Yale researchers discovered that, in people experiencing exercise intolerance, despite the heart and lungs functioning normally, the body isn’t able to properly extract and use oxygen from the blood as fuel that would normally allow a person to perform at their highest ability.
There aren’t many options for treating the condition, but doctors may prescribe high-dose vitamins and a medication used to treat muscle weakness.
Fatigue and difficulty sleeping
The 2023 preprint found excessive fatigue was experienced by 69 percent of people reporting PVS and the Yale researchers report 85 percent of people with PVS experienced the symptom.
Additionally, 70 percent of PVS patients had trouble falling or staying asleep, according to the Yale researchers.
And the 2022 UK study reported poor quality sleep among the most frequently reported side effects after receiving a Covid vaccine.
A 2023 study examining the relationship between sleep and the Covid vaccines found people who experienced vaccine side effects had less and worse sleep than people who experienced no side effects.
Thirteen percent of people had moderate to severe insomnia. Nearly four percent had trouble falling asleep; 6.8 percent couldn’t stay asleep; and 7.4 percent were consistently waking up too early.
And while brain fog is a PVS symptom itself, lack of or poor sleep can contribute to it, making it harder to concentrate and think. It can also lead to mood changes like irritability and depression and cause an increased risk of obesity, heart disease and diabetes in the long term.
Adequate sleep is crucial for the body to repair itself and for the immune system, helping to strengthen it to fend off viruses. People with PVS who suffer from poor sleep may be at a greater risk for other medical issues.
To treat sleep problems, doctors may recommend medications, talk therapy, or changes to a person’s lifestyle and diet.
Dr Lees told the Daily Mail fatigue is also one of the most common side effects of getting a vaccine but it should subside within one to two weeks.
But, if someone is still struggling with the symptom for more than six weeks, ‘supportive treatment is offered in post-viral syndrome clinics.’
Rory Nairn (pictured here), a 26-year-old from New Zealand, died from myocarditis 12 days after receiving his first dose of the Pfizer Covid vaccine in 2021
Myocarditis
Myocarditis is inflammation of the heart muscle (myocardium) that can reduce the heart’s ability to pump blood effectively, potentially leading to heart failure, abnormal heartbeat and at times, sudden death.
It is usually caused by by a viral infection and there are less than 200,000 US cases per year.
People with myocarditis may experience chest pain or tightness, shortness of breath, fatigue and loss of energy, swollen legs and irregular heartbeats.
In rare cases, mRNA shots have been shown to cause myocarditis, inflammation of the heart muscle, and pericarditis, inflammation of the sac-like lining surrounding the heart.
The side effect is rare but exactly how rare is still being debated. A major 2021 study in Israel put the rate at one in 50,000. Other studies have come to vastly different estimates.
Dr Jared Ross, an emergency medicine physician and medical school professor, told the Daily Mail post-vaccine myocarditis is more common in males than females, especially under the age of 30.
He said the condition typically develops after a viral infection, but can be triggered by a vaccine – most commonly the Moderna Covid vaccine.
CDC data shows post-vaccine myocarditis and pericarditis – inflammation of the tissue surrounding the heart – are established side effects of Covid vaccination, though the agency does not provide a number of cases.
In the conditions, it’s thought the immune system may register mRNA in Covid vaccines as a threat, leading it to attack itself and cause inflammation of the heart.
Both conditions have also been linked to Covid.
But in January 2025, Canadian experts began calling for more research into heart damage linked to Covid vaccines.
They noted that the scale of the issue remains ‘under-documented’ due to the studies being too narrow and haven’t looked at the risk of these injuries months and years after receiving the shot.
The researchers from British Columbia also warn that these studies have been inconsistent in how they classify ‘postvaccine’ myocarditis and pericarditis, using different timeframes to define if the conditions were directly linked to the shots.
Treatment for myocarditis includes medications, lifestyle adjustments, rest, surgery or a heart transplant in severe cases.
However, Dr Ross said: ‘Thankfully, most patients fully recover.’
Tinnitus is a hearing problem that most commonly takes the form of persistent ringing in the ears
Tinnitus
Tinnitus is a hearing problem that most commonly takes the form of persistent ringing in the ears. It can also sound like buzzing, roaring, hissing, or clicking.
Aside from being a nuisance and disruptive, tinnitus can cause frequent awakenings during the night, as the perceived sound becomes more noticeable in the quiet of the bedroom – disrupting the normal sleep cycle and causing insomnia and sleep deprivation.
When such sounds last more than six months, it’s known as chronic tinnitus.
A 2024 study published in Frontiers in Pharmacology that analyzed a survey of 398 cases of Covid vaccination-related tinnitus found it occurred in 47 cases per million complete vaccinations with Pfizer’s Covid shot.
There were also 51 cases of tinnitus per million complete vaccinations with Moderna’s shot and 70 cases per million complete vaccinations with J&J/Janssen’s shot.
Dr Hamid Djalilian, chief medical advisor for NeuroMed Tinnitus Clinic, told the Daily Mail the Vaccine Adverse Event Reporting System (VAERS) has about 12,000 reports of tinnitus following a Covid vaccination, ‘but compared to the millions of vaccines given, the overall rate is low.’
A team at Stanford Medicine Molecular Neurotology Laboratory is studying to find the underlying cause of tinnitus and identify people at risk of developing it after getting a vaccine.
Dr Konstantina Stankovic, an otolaryngologist-head and neck surgeon who is leading the research, told NBC: ‘We think that many forms of tinnitus reflect some damage in the inner ear and then the brain tries to compensate for the damage and starts to make sound of its own.’
The research is ongoing and findings have not been published yet.
To treat tinnitus, doctors typically prescribe steroids and one case study also saw doctors treat a patient with repetitive transcranial magnetic stimulation (rTMS) treatment, which is a noninvasive brain stimulation technique that uses magnetic pulses to adjust brain activity that may be causing the ear ringing.
Dr Djalilian said ‘the best thing is to start supportive care’ if you develop the condition following a vaccine.
He continued: ‘This includes antioxidants, hydration, and rest. Staying calm is important, as anxiety and stress only makes things worse.
Kari Ponce de Leon, a 43-year-old mother-of-two from Montana, told the Daily Mail doctors diagnosed her with a series of blood conditions that caused her immune system to block platelets.
Blood clots and low platelets
The co-occurrence of blood clots and low platelet counts following a Covid vaccination is a condition called thrombosis with thrombocytopenia syndrome (TTS).
It is a rare but serious condition that has been linked to the J&J/Janssen Covid vaccine, the CDC reported.
It involves the formation of blood clots (thrombosis) together with a decrease in platelet count (thrombocytopenia).
Blood clots can travel throughout the body and lead to deadly complications like strokes, while platelets are essential for blood to clot and for wounds to heal, so having too few could lead to uncontrolled, deadly bleeding.
Symptoms include severe headaches, blurry vision, difficulty speaking, easy bruising, leg pain or swelling, excessive bleeding and abdominal pain.
A CDC report from August 2021 stated there had been 38 cases of TTS within 15 days of Covid vaccinations and four patients had died as of July 2021.
At the time, the overall TTS rate was three cases per 1million doses.
In early 2021, the FDA and CDC recommended pausing the use of the J&J/Janssen vaccine over concerns of its connection to TTS – with six cases having been reported up until that point.
In April 2021, however, it lifted the pause after a safety review and the agencies stated the benefits outweighed potential risks.
More recent data on TTS after Covid vaccination is limited. One 2022 study found the rate was five cases per 130,000 people based on data from Norway.
This, researchers wrote, suggests an incidence of one case of TTS in 26,000 vaccinations.
The precise mechanism by which Covid vaccines cause TTS is not known, but it is believed to be set off by some sort of immune response.
Treatment for TTS includes anti-clotting medications and an infusion of blood that contains certain antibodies.
Kari Ponce de Leon, a 43-year-old mother-of-two from Montana, told the Daily Mail doctors diagnosed her with a series of blood conditions that caused her immune system to block platelets- similar to what happens with TTS.
And one doctor wrote in a letter that her condition was likely caused by the Covid vaccine ‘because he couldn’t find any other reason.’
A 2022 study led by academics at Imperial College London suggests almost 20million lives were saved by Covid vaccines in the first year since countries began rolling out the jabs, the majority in wealthy nations
Numbness or burning sensations
The 2022 UK study found one of the most frequently reported adverse events after receiving the Pfizer and Oxford-AstraZeneca vaccine was paresthesia – tingling, numbness, prickling or burning sensations throughout the body.
Additionally, the 2023 preprint found 63 percent of people with PVS reported experiencing numbness and 63 also reported neuropathy – or nerve damage that causes pain, numbness, tingling or weakness most commonly in the arms, legs and feet.
Numbness and burning sensations were also among the most common ailments suffered by PVS patients analyzed by the Yale researchers.
Eighty percent of people reported tingling and numbness and 58 percent reported burning sensations.
Treatment for these symptoms can include over-the-counter pain medications, anti-inflammatory creams, anti-anxiety and anti-convulsant medications used off-label, physical and occupational therapy and lifestyle and diet changes.
Guillain-Barré syndrome
Dr Ross explained to the Daily Mail that Guillain-Barré syndrome (GBS) is a neurological disorder in which the body’s immune system attacks and damages nerves.
It causes muscle weakness, numbness, and paralysis.
He said GBS is caused by antibodies that attack the nervous system and it typically occurs after a viral infection or a vaccine – such as the one for Covid.
Symptoms include unsteady walking, trouble with facial movements and speaking and tingling and weakness most often in the feet, legs, arms and upper body. While most patients recover, severe cases can result in paralysis or death.
However, recent studies have found evidence suggesting an increased risk of GBS among adults aged 18 and older due to the Covid vaccination.
In the August 2021 CDC report, the agency said that after 12.6million doses of the J&J/Janssen vaccine, there had been 100 reports of GBS between February and June of that year.
At the time, the rate of GBS was roughly eight cases per million J&J/Janssen vaccine doses.
A separate study from 2023 published in The Cureus Journal of Medical Science found that Covid shots like the J&J/Janssen vaccine – which is a type of vector vaccine – could make a person over twice as likely to develop GBS.
Vector vaccines use a harmless virus to deliver genetic material into the body to trigger an immune response against the targeted disease.
The researchers conducted a review of 70 studies on post-vaccination GBS and found 80 percent of the patients developed GBS within 21 days following the first dose of a vector vaccine.
Dr Lees told this website that one meta-analysis estimated the overall incidence of GBS to be four per 1million doses of an adenovirus vector vaccine.
However, Dr Lees, who is a medical writer at ZipHealth, said a Covid-19 infection itself is associated with an increased risk of developing GBS – ‘higher than any potential risk associated with vaccination.’
While scientists are yet to determine how the vaccine can trigger GBS, they noted that most of the affected patients were successfully treated and only one death was reported due to autonomic dysfunction – a condition where involuntary body functions such as heart rate, blood pressure and digestion do not function properly.
There is no direct cure for GBS and therapy concentrates on alleviating symptoms and preventing complications through blood transfusions, respiratory support and physical therapy.
