NEW YORK, April 10: A new study from the Cleveland Clinic casts doubt on the effectiveness of the annual flu vaccine, which is typically recommended for all Americans aged 6 months and older by the Centers for Disease Control and Prevention (CDC). According to the preprint study published this week on MedRxiv.org, the flu vaccine may not offer the protective effects people typically expect.

The study examined infection data for the 2024-2025 flu season, focusing on 53,402 Cleveland Clinic employees in northern Ohio. Researchers found that, among these individuals, those who received the flu vaccine actually experienced a 27% higher rate of flu infections compared to those who did not get vaccinated. The study compared vaccinated employees to non-vaccinated employees over a 25-week period.

"This study found that influenza vaccination of working-aged adults was associated with a higher risk of influenza during the 2024-2025 respiratory viral season, suggesting that the vaccine has not been effective in preventing influenza this season," the researchers wrote.

Though the findings are based on extensive data, the study has not yet been peer-reviewed and is still in its pre-print stage. The researchers also pointed out several limitations, such as the fact that nearly all (99%) of the study’s participants were given the trivalent inactivated influenza vaccine. The study suggests that other influenza vaccines might have been more effective, but this possibility has not been explored.

Additionally, the study acknowledged that home testing kits could have missed some flu infections. The study also did not measure flu-related hospitalizations or deaths, nor did it assess whether the vaccine decreased the severity of the illness.

"Our study of healthcare personnel included no children and few elderly subjects, and primarily consisted of individuals who were healthy enough to be employed," the researchers noted. "A minority would have been expected to have been severely immunocompromised."

Dr. Marc Siegel, a clinical professor of medicine at NYU Langone Health and senior medical analyst at Fox News, reviewed the study and found its findings to be misleading. "It is observational, so it does not prove that the vaccine doesn’t decrease spread," Siegel explained. He argued that the study fails to account for the fact that healthcare workers, who are more likely to be exposed to the flu due to their profession, were compared to the general population. This, he said, could lead to a higher infection rate among vaccinated workers, regardless of vaccination status.

Siegel further stated that the study misused the term "effectiveness," as the primary goal of the flu vaccine is not to reduce the spread of the virus, but to decrease the severity of illness. He explained that the true measure of flu vaccine effectiveness is the reduction in hospitalizations or doctor visits, which typically decreases by over 100,000 cases annually due to the vaccine. He also emphasized that the flu vaccine can reduce the viral load, which in turn may lower the spread of the virus within communities.

Dr. Jacob Glanville, CEO of biotechnology company Centivax, also urged caution, noting that the study has not been peer-reviewed. "We should await that process, as it will serve to check statistical methods and other study design considerations," he said. He also raised the possibility that Cleveland Clinic employees who were not vaccinated may have been discouraged from reporting their illnesses, which could skew the results. Glanville added that if this trend is accurate, it should be supported by other studies from the same flu season.

Dr. Mike Sevilla, a family physician based in Salem, Ohio, agreed with the study's suggestion that the flu vaccine this year was not as effective as expected. He pointed out that the effectiveness of the annual flu vaccine can vary greatly from year to year, ranging from 10% to 60%. While Sevilla reported seeing increased cases of influenza this season, he clarified that the cases were generally not as severe. He still encourages his patients to get the flu vaccine, as it can reduce the severity of illness even if someone does contract the flu.