Can the flu shot also backfire?

On his online show, Del Bigtree claims that a Cleveland Clinic study found people who got last year’s flu shot were more likely to catch the flu than those who didn’t, and he criticizes doctors for recommending the vaccine without knowing this, suggesting people stop trusting them.

A recent study from the Cleveland Clinic was released as a preprint. This means it hasn’t yet gone through peer review, the process where other scientists carefully check a study to make sure the research methods and conclusions are sound. Because that review hasn’t happened, the authors note that the study “should not be used to guide clinical practice.” In other words, doctors shouldn’t use the study to make medical decisions yet.

There were also other issues with the study. One big problem was selection bias, which means the people included in the study might not represent everyone fairly. For example, people who get the flu shot might be more likely to visit the doctor or get tested for the flu when they feel sick, while unvaccinated people might not get tested at all. This can make it look like more vaccinated people have the flu, even if that’s not really the case.

Another limitation is that the study only looked at how many people caught the flu, not how sick they got. But one of the main reasons people get the flu vaccine is to prevent severe illness. Even if someone still gets the flu after being vaccinated, they are usually less likely to end up in the hospital or miss a week of school or work. For instance, a vaccinated person might have a low fever and a sore throat for a couple of days, while an unvaccinated person might get a high fever and be bedridden for a week. The vaccine can also reduce the risk of dangerous complications like pneumonia, especially in older adults or people with chronic health problems.

Because the study didn’t measure these more serious outcomes, it doesn’t give the full picture of how the flu vaccine protects people. More careful research is needed before drawing conclusions about the vaccine’s effectiveness.