Experts at Yale University have discovered a potential post-vaccination syndrome linked to mRNA Covid vaccines, which may cause symptoms such as brain fog, dizziness, and exercise intolerance. The condition, still under investigation, appears to involve distinct biological changes, including altered immune cells and the presence of coronavirus proteins in the blood long after vaccination.
Findings suggest that some patients exhibit higher levels of these proteins compared to individuals with long Covid. Additionally, the syndrome appears to reactivate Epstein-Barr virus, a dormant virus that can cause flu-like symptoms, swollen lymph nodes, and nerve-related issues.
While the study is still in progress, Yale immunologist Dr. Akiko Iwasaki emphasized that it provides an initial glimpse into potential mechanisms causing these symptoms. “It’s not like this study determined what’s making people sick, but it’s the first kind of glimpse at what may be going on within these people,” she told The New York Times.
Vaccine Safety and Known Risks
Covid vaccines have saved millions of lives worldwide, with severe side effects being exceptionally rare occurring in approximately one in 200,000 cases, according to official US data. Recognized risks include myocarditis (heart inflammation) and Guillain-Barré syndrome, a condition where the immune system attacks nerves, causing pain, fatigue, and numbness.
As of December 2024, around 14,000 claims of vaccine-related injury or death had been filed with the US Covid vaccine injury compensation program, out of 270 million vaccinated Americans. However, leading experts, including Dr. Paul Offit of the Children’s Hospital of Philadelphia, stress that large-scale clinical trials and real-world data indicate the vaccines remain safe.
“The vaccines have been given to billions of people,” Dr. Offit said.
“Large prospective placebo-controlled studies didn’t show these effects. We detected myocarditis and even Guillain-Barré syndrome, which occurs at a rate of around eight in a million, so we would have identified any significant risks if they existed.”
CDC data confirms that only two serious adverse effects—anaphylaxis and heart inflammation (myocarditis or pericarditis)—have been conclusively linked to Covid vaccination.
Analysis of the Study and Next Steps
The Yale study, conducted between December 2022 and November 2023, analyzed blood samples from 42 people experiencing post-vaccination syndrome and 22 without symptoms. Researchers identified differences in immune cell proportions but have yet to correlate them with specific symptoms.
Independent experts agree that further research is needed to understand the prevalence of this syndrome and identify those most at risk. The next phase of the study will focus on determining its scope and underlying mechanisms.
While these findings highlight the importance of ongoing vaccine safety research, health officials continue to emphasize that the benefits of Covid vaccines far outweigh the risks.
