However one problem we have is that for mere side effects ("My arm aches a bit", "My period was a week late", "I feel kinda sleepy in the morning") we don't have good baseline data to compare with. I'd quite like to see someone study, e.g. if we change the Facebook blue colour slightly, and ask a study cohort, what medical "side effects" do they report for that? Clearly someone in a large survey population will report that their right thumb hurts now, and we can reason (but not prove) that's not going to be a direct result of the CSS change, but measuring what this noise looks like would provide a baseline for low risk vaccinations.
