In a groundbreaking development, researchers have begun to shed light on why a small subset of individuals experience chronic health problems following COVID-19 vaccination.

Dubbed “post-vaccination syndrome” (PVS), this rare condition has sparked curiosity and concern, prompting scientists to investigate its underlying causes.

Several mainstream news outlets, including The New York Times, Reuters, and Fox News, have reported on these emerging findings, highlighting the complexity of the issue and the need for further study.

A team from Yale University, led by immunologist Akiko Iwasaki and cardiologist Harlan Krumholz, has made significant strides in understanding PVS.

According to a February 20, 2025, article in The New York Times, the researchers studied a small group of patients and found distinct biological changes in those affected.

Some individuals with PVS exhibited higher levels of the SARS-CoV-2 spike protein—the same protein the vaccine prompts the body to recognize to build immunity—in their blood.

This persistence of spike protein has previously been associated with long COVID, suggesting a potential overlap in mechanisms.

Additionally, the study noted reactivation of the Epstein-Barr virus (EBV) and differences in immune cell profiles, such as lower levels of certain white blood cells, in those experiencing symptoms.

The New York Times emphasized that these findings, while preliminary, indicate that PVS may involve an immune system response gone awry.

Symptoms reported by affected individuals include fatigue, brain fog, exercise intolerance, insomnia, and dizziness—issues that can emerge within days of vaccination and persist for months or even years.

Iwasaki cautioned that the research is in its early stages and has not yet been peer-reviewed, but it offers a starting point for understanding this rare phenomenon.

Fox News, in a February 24, 2025, report, underscored that while the vast majority of people experience no adverse effects from the COVID-19 vaccine, a small percentage suffer from prolonged symptoms.

The outlet cited the Yale study, noting that among 42 participants with PVS symptoms and 22 without, those affected showed unique immunological patterns.

The researchers speculated that factors like autoimmunity, tissue damage, or elevated spike protein levels could contribute to the syndrome.

Dr. Marc Siegel, a clinical professor at NYU Langone Health, told Fox News that PVS is a real condition observed across various vaccines, including those for COVID-19, stressing the importance of continued investigation.

The article also quoted Krumholz, who emphasized the scientific community’s responsibility: “It’s clear that some individuals are experiencing significant challenges after vaccination.

Our job is to listen, investigate, and find ways to help.”

This acknowledgment reflects a growing awareness that while vaccines have saved millions of lives, rare side effects warrant attention.

Although Reuters did not directly report on this specific Yale study based on the provided search results, its past coverage of vaccine safety aligns with the broader narrative.

For instance, Reuters has noted that all medical interventions carry some risk, a point echoed by the Yale researchers in their discussions with other outlets.

The news agency has also highlighted the global success of COVID-19 vaccines in preventing severe illness and death, providing context for the rarity of conditions like PVS.

Experts interviewed across these reports urged caution in interpreting the findings.

John Wherry, an immunologist from the University of Pennsylvania cited by The New York Times, called the Yale team’s work rigorous but stressed that the results are not yet conclusive.

He advocated for further scrutiny to determine the scope and mechanisms of PVS, noting that shining a light on this issue could lead to better support for those affected.