Every year, millions of people roll up their sleeves for the seasonal flu vaccine, aiming to protect themselves from influenza and its complications. However, a new study from the Cleveland Clinic has stirred public concern by suggesting that vaccinated individuals might face a higher flu shot risk appearing more likely to contract influenza than those who skipped the vaccine. This finding has fueled debates across social media, prompting an important question: does getting vaccinated actually raise your flu shot risk? To understand the truth, we need to unpack what the research really found, what it didn’t, and how it fits into decades of established vaccine science.
What the New Study Found
Researchers at the Cleveland Clinic analyzed data from over fifty-thousand employees during the 2024–2025 flu season. Among the participants, about 82% received the annual flu shot. The analysis revealed that vaccinated individuals were about 27% more likely to test positive for laboratory-confirmed influenza than their unvaccinated counterparts.
At first glance, these numbers might imply that vaccination increases flu shot risk, but the researchers themselves cautioned against that interpretation. They emphasized that the study only showed an association, not causation. Many factors — from behavior differences to testing frequency — could have influenced the results.
The calculated vaccine effectiveness in this specific study was about −26.9%, suggesting that in this dataset, vaccinated participants appeared slightly more likely to test positive. However, the authors clearly stated that biases and other variables might have affected the data.
So while this study generated headlines, it did not overturn the broader scientific consensus about the benefits of flu vaccination.
Why the Study Results May Be Misleading
1. It’s a Preprint, Not Peer-Reviewed
The first and most crucial point is that this study has not yet undergone the peer-review process. Preprints are early versions of research that haven’t been formally checked by other scientists. They can be useful for sharing new ideas quickly, but they may contain errors, oversights, or misinterpretations that are later corrected.
Without peer review, conclusions about flu shot risk drawn from this data remain provisional and subject to change.
2. Testing Bias: Who Gets Tested More Often?
One of the strongest explanations for the observed difference is testing bias. Vaccinated individuals, especially healthcare workers, are often more health-aware and more likely to seek medical care or testing when they feel ill.
If vaccinated people get tested more frequently than unvaccinated ones, the rate of confirmed infections will naturally appear higher among them — even if the actual number of infections is the same or lower.
Thus, differences in behavior and healthcare access can easily distort estimates of infection rates and create the illusion of higher flu shot risk.
3. A Non-Representative Population
The study focused exclusively on employees of the Cleveland Clinic — a unique group that includes healthcare professionals, administrators, and staff. These individuals are generally younger, healthier, and more health-conscious than the general population.
Moreover, many of them are required or strongly encouraged to get the flu vaccine as a condition of employment. The unvaccinated group may differ in lifestyle, exposure, or job roles. Because of these differences, results cannot be generalized to the wider public.
When considering flu shot risk, context matters — what applies to a hospital workforce does not necessarily apply to the general community.
4. Strain Mismatch and Seasonal Variability
Each year, flu vaccines are reformulated to match the predicted circulating strains of the influenza virus. Sometimes the match is excellent, and vaccines are highly protective. Other times, the circulating strains differ significantly, leading to lower effectiveness.
In years of poor match, even well-designed studies may find limited or negative vaccine effectiveness. This does not mean the vaccine increases flu shot risk it simply reflects a mismatch between vaccine and virus strains.
Vaccine effectiveness varies season to season, but over time, data consistently show that vaccination reduces severe outcomes, even when infection rates fluctuate.
5. The Study Didn’t Measure Severity
Another important point is that the Cleveland Clinic study measured only infection rates — not severity. It did not assess whether vaccinated individuals had milder symptoms, fewer hospitalizations, or reduced complications compared to unvaccinated ones.
The main goal of the flu vaccine is not to guarantee complete immunity but to reduce the risk of serious illness, hospitalization, and death. Even in years when protection from infection is modest, vaccination can significantly reduce disease severity.
Hence, using infection rates alone to judge flu shot risk is misleading and incomplete.
What Broader Scientific Evidence Says
While one study may spark controversy, vaccine safety and effectiveness are evaluated based on decades of data involving millions of people worldwide. The overall picture is clear: influenza vaccination provides substantial benefits in most seasons.
1. Effectiveness in Reducing Illness and Hospitalization
Long-term surveillance by major health agencies shows that flu vaccines typically reduce the risk of medically attended influenza illness by 40–60% when the vaccine strains closely match circulating viruses.
Even in seasons with poor matches, vaccination still helps lower the risk of hospitalization and severe complications. These outcomes contradict the idea that flu shot risk outweighs benefit.
2. Protection Against Secondary Infections
Studies examining household transmission demonstrate that vaccinated individuals are less likely to spread influenza to close contacts. When one family member catches the flu, vaccinated relatives are generally less likely to become ill compared to unvaccinated ones.
This indirect benefit — known as “herd protection” — further decreases community spread and lowers overall infection burden, again undermining claims of higher flu shot risk.
3. Vaccine Interference and Immunity
Some scientists have investigated whether receiving one vaccine could influence the immune system’s response to other viruses — a concept called “vaccine interference.” While some early studies hinted at mild effects, larger meta-analyses have found inconsistent results.
No strong evidence shows that the flu vaccine suppresses the immune system or increases general susceptibility to infection. Mechanistically, vaccines enhance immune readiness rather than weaken it.
Thus, biologically, there is no plausible reason to believe that vaccination elevates flu shot risk across populations.
Putting the Findings in Perspective
To understand whether flu vaccines might raise infection risk, it’s important to distinguish between correlation and causation. A correlation means two factors occur together — like vaccination status and infection — but it doesn’t mean one causes the other.
The Cleveland Clinic study found a correlation but did not demonstrate causation. Differences in who gets tested, exposure rates, and timing could easily explain the observed pattern.
When the totality of evidence is considered, flu vaccination continues to show benefits far greater than any potential flu shot risk. The rare findings of negative effectiveness are anomalies usually linked to specific biases or mismatched vaccine strains.
The Real Risks: Myths vs. Facts
There are many misconceptions about flu vaccines that contribute to confusion. Let’s clarify a few common myths surrounding flu shot risk:
- “The flu shot gives you the flu.”
False. The vaccine uses inactivated or weakened virus components that cannot cause influenza infection. - “Vaccines are unnecessary for healthy adults.”
Incorrect. Even healthy people can get severe flu or spread it to vulnerable individuals such as the elderly, pregnant women, or those with chronic illnesses. - “Flu vaccines don’t work.”
Effectiveness varies but even partial protection reduces illness severity and transmission. - “It’s better to get natural immunity.”
Natural infection can lead to complications such as pneumonia or hospitalization. Vaccination provides safer, controlled immunity without those dangers.
Understanding these facts helps put perceived flu shot risk into context and supports informed decision-making.
Public Health Perspective
From a population standpoint, influenza vaccines remain one of the most effective preventive tools available. Even moderate reductions in infection and hospitalization translate into thousands of lives saved each year.
Health agencies around the world — including the CDC, WHO, and Public Health England — continue to recommend annual vaccination for all eligible adults and children over six months of age.
The benefits far outweigh any theoretical or situational flu shot risk observed in isolated studies.
How to Talk About Vaccine Studies Responsibly
The controversy around this study highlights how easily scientific nuance can be lost in public discussion. To communicate responsibly:
- Avoid overstating single studies.
One dataset cannot redefine vaccine science built on decades of research. - Clarify what outcomes matter.
Preventing severe illness, hospitalization, and death is more critical than preventing every mild infection. - Encourage critical reading.
Ask whether a study was peer-reviewed, how large the sample was, and whether it adjusted for bias. - Acknowledge uncertainty honestly.
Science evolves — some years vaccines work better than others — but the direction of benefit remains clear. - Reinforce trust in science.
Transparency and open discussion help counter misinformation about flu shot risk and vaccine safety.
Future Research Directions
The current debate shows that continued research is vital. Future studies should focus on:
- Randomized controlled trials that minimize bias.
- Diverse populations, including older adults and children.
- Adjusting for behavioral and occupational factors.
- Evaluating not just infection but also severity and long-term outcomes.
- Investigating immune response patterns across different vaccine types.
Such studies can clarify whether observed anomalies reflect real biological effects or statistical noise. Understanding this will help refine vaccination strategies and address concerns about flu shot risk in a scientific manner.
Conclusion
The Cleveland Clinic study raised important questions but did not overturn decades of research supporting flu vaccination. While it found an association suggesting higher infection rates among vaccinated workers, the findings are best explained by testing bias, population differences, and strain variability — not by a causal increase in infection risk.
Decades of data continue to demonstrate that the flu shot reduces illness severity, hospitalization, and death. In other words, the benefits of vaccination far exceed any hypothetical flu shot risk.
As scientists and public health experts often emphasize, one study does not change the fundamental truth: vaccines remain one of the most powerful and cost-effective tools for preventing disease and saving lives.
Sources
- PolitiFact, What vaccine skeptics are getting wrong about a new Cleveland Clinic study on the flu vaccine
- Al Jazeera, Fact check: Does a new study say the flu vaccine is dangerous?
- CDC, New Study Suggests Flu Vaccination Likely to Have a Substantial Public Health Impact, Prevent Millions of Medical Visits
- JAMA Network Open, Estimated Effectiveness of Influenza Vaccines in Preventing Secondary Infections in Households
- medRxiv, Effectiveness of the Influenza Vaccine During the 2024-2025 Respiratory Viral Season
