Did Cleveland Clinic study on the flu vaccine show those vaccinated caught more flu infection

1. What the Cleveland Clinic paper actually reported

The study followed 53,402 Cleveland Clinic employees from Oct. 1, 2024, through March/April 2025 and found that 82.1% received seasonal influenza vaccine during the period; overall influenza positivity was about 2.02% and the vaccinated group had a higher incidence than the unvaccinated, yielding an estimated vaccine effectiveness of −26.9% ^[1]. The authors concluded they “were unable to find a protective influence of influenza vaccination among working‑aged adults” during that season and that vaccination was “associated with a higher risk of influenza when influenza activity was high” ^[5].

2. Preprint status matters — correlation ≠ causation

The paper was posted to medRxiv as a preprint and had not completed external peer review at the time it circulated; fact‑checking outlets and the Cleveland Clinic emphasized that an observed association in an observational study is not proof that vaccination caused increased infections ^{[5] [3]}. Lead Stories summarized that the study “found that influenza vaccination ... was associated with a higher risk” but did not establish causality, and the Clinic told media the results “do not suggest that vaccination increases the risk of flu” ^{[3] [2]}.

3. Why experts and communicators warned about bias

Multiple public‑health and medical commentators raised concerns that testing bias, differences in health‑seeking behavior, occupational exposures, timing of vaccination, and other confounders could explain the counterintuitive result—rather than the vaccine increasing susceptibility ^{[2] [4] [6]}. MedPage Today’s critique described methodological problems and argued the authors “forgot how to do science,” saying the study’s design and interpretation were insufficient to support sweeping conclusions about vaccine harm ^[4]. Public health communicators warned the preprint was being used by skeptics to mislead the public ^[6].

4. How the finding was used and misused in media and social media

After the preprint appeared, headlines and social posts ran with claims such as “get the shot, get the disease,” and several outlets amplified the negative effectiveness figure without the methodological caveats; fact‑checkers and public‑health groups then pushed back, stressing the study was not peer‑reviewed and did not prove causation ^{[7] [2] [6]}. Lead Stories and others pointed out that some groups transformed the association into an assertion that the vaccine increases flu risk, which the study authors and Cleveland Clinic denied ^{[3] [2]}.

5. Broader context: vaccine effectiveness is variable by season and population

Independent reporting and Cleveland Clinic’s other vaccine research show that vaccine performance changes by strain match, vaccine type and host factors; separate Cleveland Clinic research has explored age‑specific responses and immune cell factors that influence protection ^{[8] [9]}. Public‑health bodies have long noted that seasonal effectiveness can be low some years but that vaccines still reduce severe outcomes in many settings—available sources do not mention definitive national guidance changes prompted by this single preprint ^{[8] [1]}.

6. What to watch next and how to interpret these results responsibly

Look for peer review of the preprint, independent analyses controlling for testing and exposure bias, and statements from health authorities; several outlets urged caution and said there was no reason to change vaccination recommendations based only on this report ^{[1] [2] [6]}. The story’s immediate lessons are clear: a large observational association warrants investigation, but it cannot, on its own, justify claims that the flu shot causes more infections ^{[3] [4]}.

Limitations and caveats: this analysis uses only reporting and commentary in the supplied sources. Available sources do not mention randomized‑trial confirmation that the 2024–25 vaccine increased infection risk.