Experts from Yale University have discovered an alarming syndrome linked to the mRNA Covid vaccines.

The previously-unknown condition - dubbed 'post-vaccination syndrome' - appears to cause brain fog, dizziness, tinnitus and exercise intolerance.

Some sufferers also show distinct biological changes, including differences in immune cells and the presence of coronavirus proteins in their blood, years after taking the shot.

The condition also appears to reawaken a dormant virus in the body called Epstein-Barr which can cause flu-like symptoms, swollen lymph nodes and nerve issues.

The full results of the small study have not yet been published, and the Yale experts emphasized the results 'are still a work in progress.'

Yet the findings, from a well-respected institution, suggest more research on post-vaccination syndrome is needed, independent experts said.

The next phase of the research will be to ascertain how widespread the condition is and who is most at risk.

Thousands of people have said that Covid vaccines injured them since the shots were rolled out in 2021.

But the fragmented nature of the US healthcare system makes it challenging to identify rare side effects.

Larger studies have failed to separate the symptoms suffered after Covid vaccination from unrelated illnesses that would have occurred regardless.

Dr Akiko Iwasaki, study author and immunologist at Yale University, said: 'This work is still in its early stages, and we need to validate these findings.

'But this is giving us some hope that there may be something that we can use for diagnosis and treatment of PVS down the road.'

The mRNA vaccines made by Moderna and Pfizer are estimated to have saved tens of millions of lives globally from Covid, including 3million in the US.

In the new study, which has not been peer-reviewed, Iwasaki's team collected blood samples from 42 people with post-vaccination syndrome (PVS) and 22 people without it between December 2022 and November 2023.

When they analyzed the patients' immune systems, those with PVS had different proportions of some immune cells. It’s unclear what these differences might mean as the researchers couldn't link them to specific symptoms.

The team also looked at 134 people with long Covid, as PVS symptoms overlap with it, as well as 134 healthy vaccine recipients. 

Both people with long Covid and those with PVS seemed to have reactivated Epstein-Barr syndrome.

More than nine in 10 adults have had Epstein-Barr at some point in their lives, a common infection spread through bodily fluids like saliva or semen. 

It causes symptoms like fatigue, fever, and rashes, and once symptoms disappear, the virus remains dormant in the body, where it can be reactivated when the immune system is low.

People with PVS also had elevated levels of Covid spike proteins.

The levels in PVS patients were even greater than those found in patients with long Covid, a condition with similar symptoms linked to the virus itself.

Persistent spike proteins in the body are thought to cause some of long Covid's symptoms, by keeping the body in a constant state of inflammation.

This was true in patients who received their vaccines between 36 and 709 days prior. 

Dr Iwasaki said: 'That was surprising, to find spike protein in circulation at such a late time point.

'We don’t know if the level of spike protein is causing the chronic symptoms, because there were other participants with PVS who didn’t have any measurable spike protein. 

'But it could be one mechanism underlying this syndrome.'

The study's main limitation was its small size, Dr Gregory Poland, emeritus editor of the journal Vaccine and president of Atria Research Institute, told the New York Times. 

However, he added: 'Despite these limitations, they found interesting data that need further study.

'Much larger studies of very carefully defined and phenotyped individuals [genetically analyzed] need to take place.'

Dr Harlan Krumholz, co-senior study author and Harold H. Hines, Jr. Professor of Medicine at Yale, said: 'It’s clear that some individuals are experiencing significant challenges after vaccination. 

'Our responsibility as scientists and clinicians is to listen to their experiences, rigorously investigate the underlying causes, and seek ways to help.'

Dr John Wherry, director of the Institute for Immunology at the University of Pennsylvania who was not involved in the research, urged caution about the data and said it's possible some of the excess spike protein may be from undetected Covid infections.

He told The New York Times: 'I would like to see more data on this topic.' 

The mRNA vaccines made by Moderna and Pfizer are estimated to have saved tens of millions of lives globally, including 3million in the US.

Data from the US Covid vaccine injury compensation program suggested that 14,000 people had filed claims for injury or death they claimed were caused by the Covid vaccine as of December 2024, out of the 270million Americans who received at least one dose of the vaccine.

Dr Paul Offit, a vaccines expert at the Children's Hospital of Philadelphia, told DailyMail.com this highlighted that the vaccines were not dangerous.

He said: 'The vaccines have been given to billions of people at this point, and there were large prospective placebo-controlled studies that didn't show these effects.

'As the vaccines were rolled out, not everyone got them at once... and this staggering would tell you if something is a problem that was not picked up in clinical trials.'