Did Yale Scientists Find COVID-19 Spike Proteins in Vaccinated People? What We Know About Rumor

In December 2024, a rumor began spreading online that a team of researchers at Yale University had found the "spike protein" of the SARS-CoV-2 virus, which is responsible for the COVID-19 illness, in the blood of people who had never been infected but had been vaccinated.

Social media users shared this claim and suggested it was alarming because it meant the genetic material of the vaccine had "integrated" with human DNA.

For example, on Dec. 21, 2024, one X user said (archived): "URGENT: Yale researchers have found Covid spike protein in the blood of people never infected with Covid - years after they got mRNA jabs. The spike proteins shouldn't be there. It's possible that vaccine genetic material has integrated with human DNA, causing long-term spike production."

Several posts repeated the same claim, and many linked to one report on Substack, written by Alex Berenson. Berenson is a former reporter at The New York Times who has been described as a "vaccine skeptic" due to his accounts of the COVID-19 pandemic and the responses to it. According to The Atlantic, he made numerous disproved assertions during the pandemic. Likewise, fact-checking outlet PolitiFact gave a "false" rating to a claim linked to Berenson that the Centers for Disease Control and Prevention (CDC) had said more young people had been hospitalized from the COVID-19 vaccine than the virus itself.

Berenson's Substack report was titled: "URGENT: Yale researchers have found Covid spike protein in the blood of people never infected with Covid - years after they got mRNA jabs."

He was referring to a 2022 study — launched by a team at Yale and led by immunobiologist Akiko Iwasaki — to track the effects of long COVID in an effort to associate symptoms to biological markers (biological molecules found in bodily fluids that indicate normal or abnormal processes, such as illness). They began by recruiting patients with self-reported long COVID symptoms and later added patients with self-reported post-vaccination syndrome (PVS) to the study. They named this study LISTEN, which stands for Listen to Immune, Symptom and Treatment Experiences Now. 

Participants are invited to report on their health status and all factors that might contribute to it, including demographics, clinical history, social life and the environment. Some participants are then asked to send in blood and saliva samples. Participants are also invited to take part in video "town halls," in which the team shares its preliminary findings. Some of these town halls are widely accessible online while others are not. 

In his report, Berenson cited two anonymous sources for his claim. One of them, he said, is a participant in the study and "directly heard the reports from the Yale researchers on the conference call," while the other is a scientist who is not part of the Yale team but is allegedly in contact with some of its members.

What are spike proteins?

Spike proteins cover the surface of the SARS-CoV-2 virus, giving it its crown ("corona") aspect. These spikes bind to human cells in order to infect them. The spikes themselves do not cause the illness, but they do enable it. However, spike proteins are the ones scientists used to develop the Pfizer and Moderna messenger RNA (mRNA) vaccines.

The vaccines place small strands of mRNA with the genetic code for the spike proteins into the body. Those strands of mRNA penetrate certain human cells, known as dendritic cells, which begin to produce spike-like proteins, which spread throughout the body. Later, immune cells use these proteins to produce antibodies that will block the actual virus' spike proteins from binding to people's cells and infecting them.

How an anti-vaxxer's speculation went viral

The finding, as outlined by Berenson, is that the team found spike proteins in the blood of vaccinated people who had never been infected by the virus. One of them had received their last jab more than 700 days prior and others had received their last jabs more than 450 days prior. This, Berenson speculated, could mean that the body itself was producing spike proteins after the genetic material "integrated" with human DNA.

Berenson's speculation spread widely online among vaccine skeptics. However, he added a caveat to his report by saying that the team at Yale had brought forth no proof that the genetic material had "integrated" with the DNA. In fact, lower in his report, he said this would be "unlikely." Further, he added that the appearance of the spike protein in participants' samples may not have medical relevance:

To be clear, the finding does not provide definitive proof of genetic integration, or what researchers call "transfection." For that, researchers must extract DNA from human cells and find the genetic sequences the vaccine delivers. How frequently the spike protein is appearing and whether the levels might have clinically significant consequences are also unclear.

Rather, he speculated that there may have been some "vaccine batches with more DNA contaminant" early in the distribution of new mRNA vaccines.

The study

On Feb. 19, 2025, the Yale team released the results of their study, which had not yet been reviewed by peers. The study, which included 42 people with self-reported PVS and 22 other healthy participants as controls, concluded that those with PVS showed a similar immune profile, with a reduced number of antibodies against the virus' spike protein, which could be explained by the fact that they had received fewer doses of the vaccine. 

Further, they found that "a subset" of participants with PVS — including among those who did not present markers of prior COVID-19 infection — had higher levels of the virus' spike protein compared to controls. "Typically spike protein can be detected for a few days after vaccination, but some participants with PVS had detectable levels more than 700 days after their last vaccination," a Yale News report on the study read. "Persistent spike protein has been associated with long COVID as well."

However, it is unclear whether the spike protein is at the root of the symptoms. "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," Iwasaki told Yale News. "But it could be one mechanism underlying this syndrome."

The study further showed that participants with PVS were more likely to show signs of reactivation of the Epstein-Barr virus, a virus of the herpes family that causes mononucleosis. Once infected with EBV, a person cannot clear it, but the virus may go dormant, reactivating occasionally. "Serological evidence of recent Epstein-Barr virus (EBV) reactivation was observed more frequently in PVS participants," the study article read. This could be an indication that EBV may be one of the factors causing the symptoms of PVS.

In response to the study, Berenson updated his newsletter, saying "I first wrote about that finding in December, but it looks even more serious now that the preprint is out." However, he added that due to the fact that the Yale team did not take blood samples from the participants before they received their vaccines, "for now they cannot prove the jabs caused any immune dysfunction." Berenson does not mention the Yale team's findings about EBV and other possible causes for PVS in his update.

Indeed, Iwasaki and her team warned that their findings needed validation, and that more studies should take place, as their sample size was quite small. 

Snopes contacted the team at Yale via email for more clarification. We will update this report should they reply.