New research reveals startling link between long COVID and post-vax syndrome
Key Takeaways
Industry Buzz
“Epstein-Barr virus, which infects most adults and typically remains dormant, has been shown to reactivate in approximately two-thirds of long COVID patients.” — Amir Hadanny, MD, PhD, chief medical officer and head of research at Aviv Clinics
Research about long COVID is ongoing. A small, preliminary 2025 paper published by Yale University School of Medicine identified biological changes that could link specific symptoms of long COVID to similar symptoms observed in some cases of post-vaccination syndrome.[]
The study examined the immune cells of people with post-vaccination syndrome. Researchers found lower levels of effector CD4 T-cells and higher levels of tumor necrosis factor–secreting CD8 T-cells.
Related: How long COVID is cutting HCP careers shortMore about the study
The patients had lower levels of antibodies against the SARS-CoV-2 spike protein when compared with healthy controls. Researchers posited this was because the study patients had stopped getting additional vaccine doses.
Signs of recent Epstein-Barr (EBV) reactivation were more frequently exhibited in patients with post-vaccine syndrome.
“Research suggests a significant connection between viral reactivation and long COVID. SARS-CoV-2 appears to create immune dysregulation that can disrupt the body's ability to control latent viruses,” says Amir Hadanny, MD, PhD, chief medical officer and head of research at Aviv Clinics. “Epstein-Barr virus, which infects most adults and typically remains dormant, has been shown to reactivate in approximately two-thirds of long COVID patients,” he adds.
A group of studied patients had higher levels of an S1 spike protein in their blood. Detectable levels could be seen up to 709 days after the most recent known exposure. Continually high levels of spike proteins are another known factor in long COVID.
Long COVID and rare syndrome overlap
Patients with long COVID often experience symptoms such as neurological issues or exercise intolerance.
Dr. Hadanny walks us through some symptoms: “Long COVID typically presents with several key complications,” he says. These complications include profound fatigue unrelieved by rest, cognitive dysfunction, and persistent shortness of breath.
Cardiovascular abnormalities are also prevalent, including heart palpitations and postural orthostatic tachycardia syndrome (POTS), Dr. Hadanny explains.
Related: What balance could mean for heart and brain healthNeurological symptoms represent another significant complication, ranging from headaches and dizziness to dysautonomia, which disrupts the autonomic nervous system's normal functioning, according to Dr. Hadanny.
Patients with post-vaccination syndrome experience many of these same symptoms. The Yale study researchers suggest that this symptom overlap is linked to pathological drivers, such as EBV reactivation or spike protein.
Diagnostics
Research on long COVID and post-vaccination syndrome is still in its infancy. There are no definitive tests for diagnosing long COVID. []
Instead, diagnosis is based on a thorough review of symptoms, patient history, and data that could point to or rule out other conditions.
More diagnostic and treatment tools will likely become available as research continues to emerge.
Read Next: We just found out why women have a higher risk for long COVID