Inactivated Influenza Vaccine is a Risk to Public Health: Cleveland Clinic Study Finds Thimerosal-Containing Vaccine Increases Risk of Influenza Infection by 27%

Negative Vaccine Effectiveness in Working-Age Adults Raises Alarms About Current Flu Shot Strategy. Over 98% of the Patients Received Thimerosal-Containing Inactivated Influenza Vaccine.

A major prospective cohort study from the Cleveland Clinic has delivered a direct challenge to prevailing public health dogma: this season’s influenza vaccine was not just ineffective—it was associated with a statistically significant increase in risk of infection.

Among 53,402 working-age healthcare employees tracked over the 2024–2025 respiratory viral season, those who received the flu vaccine had a 27% higher risk of contracting laboratory-confirmed influenza compared to those who remained unvaccinated. The authors calculated a vaccine effectiveness of –26.9%, meaning the vaccinated were significantly more likely to become infected.

This is not a theoretical or model-based projection. It is real-world data from one of the most respected medical institutions in the United States, published April 4, 2025, on medRxiv.

Adjusted Hazard Ratio (HR): 1.27
95% Confidence Interval: 1.07–1.51
P-value: 0.007

At a time when public trust in medical institutions is precarious, a vaccine-induced increase in infection risk—especially in a population with near-universal compliance—undermines both policy and credibility.

Study Design: Robust and Transparent

Led by Dr. Nabin Shrestha, the Cleveland Clinic study followed a rigorous design. All employees working at Cleveland Clinic’s Ohio locations as of October 1, 2024, were included. Vaccination status was tracked as a time-dependent covariate, a crucial design choice that allowed researchers to account for changing exposure status during the season.

Employees were even considered “vaccinated” via a delay of seven days after receiving the inactivated trivalent vaccine. That type of delay led, after two doses, to a severe overestimation bias of COVID-10 mRNA injections (the Lyons-Weiler/Fenton/Neil effect). The endpoint was laboratory-confirmed influenza infection via molecular testing (nucleic acid amplification tests for influenza A or B). The median age of participants was 42, and the cohort was predominantly healthy and employed—precisely the demographic targeted by influenza vaccination campaigns.

By the end of the season, 82.1% of employees had been vaccinated, and 1,079 confirmed influenza infections were identified—98.8% due to influenza A. Yet infection rates rose faster among the vaccinated.

This finding was not a fluke: It held under both unadjusted and adjusted Cox proportional hazards models.

Explaining the Negative Effectiveness

The authors did not speculate irresponsibly, but they did highlight several possibilities: strain mismatch, immune interference, or immunological imprinting could all play roles. The most likely explanation involves immune modulation caused by the vaccine—where prior exposure via vaccination may reduce the immune system’s capacity to respond to circulating strains, especially when strain mismatch is present.

The formulation administered to nearly all participants (98.7%) was the inactivated trivalent influenza vaccine, which contain thimerosal, a mercury-based preservative still used in many multi-dose flu vials. Thimerosal is 50% ethyl mercury by weight and has much more durable brain toxicity than methyl mercury, the type environmentalists are concerned about from other sources of isolated mercury (Burbacher et al. 2005).

This finding is not without precedent. In 2012, Cowling et al. published a randomized controlled trial in Clinical Infectious Diseases showing that children who received the inactivated flu vaccine had a significantly increased risk of non-influenza respiratory virus infections:

“Receipt of TIV was associated with an increased risk of virologically-confirmed non-influenza infections (RR 4.40; 95% CI: 1.31 to 14.8).”
— Cowling BJ et al., 2012

Though the mechanisms may differ, the principle is the same: vaccination can, under certain circumstances, impair the broader immune response.

Why This Study Matters

This is one of the most consequential influenza vaccine studies published in recent years for several reasons:

1. Sample Size: Over 53,000 participants.

2. Real-World Design: A prospective cohort, not a “test-negative” case-control study.

3. Risk-Based Outcome: The study calculates risk, not just odds—avoiding the overestimation typical of odds ratio-based studies.

4. Robust Statistical Methods: Time-dependent covariates, multivariable regression, no violations of proportional hazards assumptions.

5. No Industry Funding: The authors report no conflicts of interest, and no funding was declared.

It is rare to see a study of this scale, clarity, and independence produce a result so directly at odds with national vaccine policy.

What This Means for Policy

The implication is stark: routine annual influenza vaccination for working-age adults—at least with this formulation—may not be justified under current strain selection and manufacturing models.

It also raises broader questions:

• Are we underestimating the frequency and impact of negative vaccine effectiveness in years with strain mismatch?

• Have policies like mandatory flu vaccination for healthcare workers outpaced the evidence?

• Are we adequately surveilling the real-world performance of these vaccines after deployment?

This study calls into question the wisdom of universal flu vaccine campaigns that fail to deliver consistent benefit—and may cause net harm.

A Path Forward

The authors emphasize the importance of yearly effectiveness monitoring, a point public health agencies have failed to prioritize. But this result goes further: it highlights the urgent need for transparency, mechanistic research, and a re-evaluation of assumptions surrounding influenza vaccination policy.

At a minimum, policy updates at HHS should now include:

• Banning thimerosal-containing influenza vaccines, or

• Labeling inactivated, thimerosal-containing influenza vaccines as follows: “This Product Could Increase Your Risk of Influenza”.

Future studies must:

• Examine the risk of hospitalization and death following influenza vaccination in stratifying outcomes by vaccine formulation (e.g., thimerosal vs. thimerosal-free, trivalent vs. quadrivalent) vs. unvaccinated (stratified by never-vaccinated, ceased by years ago).

• Investigate the possibility of immune interference and suppression.

• Reassess the predictive validity of strain selection methods.

• As we have called for many times before, study the effects of removing unsafe epitopes and avoiding all forms of aluminum on influenza-vaccine related adverse events.

Until then, it is no longer scientifically defensible to speak of the flu vaccine as a settled intervention for healthy adults. Evidence, not consensus, must lead.

References
Shrestha NK, Burke PC, Nowacki AS, Gordon SM. Effectiveness of the Influenza Vaccine During the 2024-2025 Respiratory Viral Season. medRxiv. Posted April 4, 2025. https://doi.org/10.1101/2025.01.30.25321421

Cowling BJ, et al. Increased Risk of Noninfluenza Respiratory Virus Infections Associated With Receipt of Inactivated Influenza Vaccine. Clin Infect Dis. 2012;54(12):1778-1783.

Burbacher, T. M., Shen, D. D., Liberato, N., Grant, K. S., Cernichiari, E., & Clarkson, T. (2005). Comparison of blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal. Environmental Health Perspectives, 113(8), 1015–1021. https://doi.org/10.1289/ehp.7712