Yale scientists link Covid vaccines to alarming new syndrome causing ‘distinct biological changes’ |

The COVID-19 vaccines have been crucial in preventing millions of deaths during the pandemic. However, post-vaccination, a few reported some side effects such as fatigue, exercise intolerance, brain fog, tinnitus, and dizziness. A recent study by Yale researchers has delved deep into this little-understood, persistent condition, referred to as post-vaccination syndrome (PVS).
In the study posted online, the researchers have characterized this condition and also studied the immunological patterns that differentiate those with PVS from others.
“This work is still in its early stages, and we need to validate these findings,” Akiko Iwasaki, Sterling Professor of Immunobiology at Yale School of Medicine (YSM) and co-senior author of the study published Feb. 19 as a preprint on MedRxiv said in a release. “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 chronic symptoms of PVS include:

These symptoms develop shortly after vaccination, which is within a day or two, and can get more severe in the days that follow.

“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,” Harlan Krumholz, the Harold H. Hines, Jr. Professor of Medicine (Cardiology) at YSM and co-senior author of the study adds.
Researchers analyzed blood samples from people in their Listen to Immune, Symptom, and Treatment Experiences Now (LISTEN) study to understand long COVID and post-vaccine syndrome (PVS). They compared 42 people with PVS symptoms to 22 people without symptoms after COVID-19 vaccination.
They found differences in immune cells between the two groups. Those with PVS had lower levels of effector CD4+ T cells and higher levels of TNF-alpha+ CD8 T cells — both are types of white blood cells — among other differences.
They also found differences in antibody levels. People with PVS who never had COVID-19 had lower levels of antibodies against the virus’s spike protein. This was likely because they received fewer vaccine doses than those without PVS. With fewer shots and no prior infection, their immune systems had less chance to build protection against the virus.
Additionally, they found that some people with PVS had higher levels of the SARS-CoV-2 spike protein, even if they had never been infected. Normally, the spike protein stays in the body for only a few days after vaccination, but in some PVS cases, it was still present more than 700 days later. This lingering spike protein has also been linked to long COVID.
“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,” Iwasaki noted.
Krumholz further added that PVS might be similar to other infections that lead to chronic symptoms, each through different biological pathways. “One person might develop chronic symptoms due to immune dysregulation, while another experiences lingering effects from viral reactivation. We need to map these different pathways carefully to understand what is happening in each case. This work is just beginning, and further studies are essential to guide diagnosis and treatment,” he said.

The researchers added that a deeper understanding of PVS is required to make better vaccines, with fewer side effects. “For instance, if we can determine why spike protein is persisting for as long as it is in some people, maybe we can remove it — with monoclonal antibodies, for example — and maybe that could help reduce PVS symptoms,” Iwasaki, a professor of dermatology and of molecular, cellular, and developmental biology in Yale’s Faculty of Arts and Sciences, a professor of epidemiology at Yale School of Public Health, and an investigator of the Howard Hughes Medical Institute added.
“We’re only just starting to make headway in understanding PVS. Every medical intervention carries some risk, and it’s important to acknowledge that adverse events can occur with vaccines. Our focus must remain on understanding what these people are experiencing through rigorous science and addressing the needs of those affected with compassion and an open mind,” Krumholz added.