Reason: College grads are more likely to get vaccinated against COVID than non-grads. Leading to a reduction in symptom severity and perhaps long covid.
https://healthpolicy.usc.edu/evidence-base/education-is-now-...
The reason I say placebo is because any of these pre-existing conditions could be blamed on long COVID. Think about it: you don't know much about diseases, you see CNN/Fox News/MSNBC talking about long COVID. You think to yourself, hey I've got those symptoms! You blame long COVID, even though the underlying cause could have been obesity, diabetes, sedentary lifestyle, diet, etc.
We know obesity is harmful yet the fat acceptance movement exists. Do you think those people are going to blame their symptoms on their obesity?