Flu vaccine linked to higher infections, says early research

The preprint study, which was published on MedRxiv.org this week, looked at infection data for the 2024-2025 flu season.

Vaccinated employees were compared to those who did not get the vaccine over a 25-week period.

While previous work by these researchers on vaccine effectiveness has been published in major journals, this most recent study is still in the pre-print stage, which means it has not yet been peer-reviewed.

The researchers noted several limitations of the study, including that "trivalent inactivated influenza vaccine" was used in about 99% of the included employees.

"The possibility that other influenza vaccines might have been more effective cannot be excluded," they wrote.

It is also possible that home testing kits might have missed some infections.

Additionally, the study did not compare the risk of flu-related hospitalizations or deaths, nor did it measure whether the vaccine decreased the severity of illness. 

Dr. Marc Siegel, clinical professor of medicine at NYU Langone Health and Fox News senior medical analyst, reviewed the study findings and said the results are "misleading."

"It is observational, so does not prove that the vaccine doesn't decrease spread," he told Fox News Digital.

Siegel also said he believes the study misuses the word "effectiveness." 

"The flu vaccine is intended to decrease severity rather than decrease spread," he noted. 

"The real yardstick for flu vaccine effectiveness is the rate of hospitalization or visit to a doctor's office or urgent care, which is usually down by well over 100,000 per year or more due to the vaccine." 

This effectiveness varies year to year based on how well the vaccine fits the predominant strain, the doctor added.

Dr. Jacob Glanville, CEO of Centivax, a San Francisco biotechnology company, echoed that the study has not yet undergone peer review.

"We should await that process, as it will serve to check statistical methods and other study design considerations," he told Fox News Digital.

"For example, it would be important to rule out reporting avoidance by non-vaccinated Cleveland Clinic employees. Did they have any policies that would discourage non-vaccinated subjects to report illness?"

"I wouldn't think that this is expected. However, in comparing previous years, the effectiveness of the annual flu vaccine can vary widely, from about 10% up to about 60%," he said in an interview with Fox News Digital.

Sevilla shared that in his office, he did see increased cases of influenza this season, but not necessarily as severe cases. 

"I still tell my patients that a benefit from receiving the flu vaccine is that even though you may get the flu, your case may not be as severe as those who did not receive the flu vaccine," he said.

"If you have any questions about vaccines, you can always ask your family physician."

Fox News Digital reached out to the Cleveland Clinic researchers for comment.