One person's experience = anecdotal.
10,000 or 100,000 or 1,000,000 people's experiences = epidemiological evidence.
There are people who smoke 2 packs of cigarettes a day and don't get lung cancer or emphysema or heart disease = anecdotal. There are non-smokers who get lung cancer = anecdotal. When you look at the entire USA population of over 300,000,000 people, smokers get lung cancer at 11 times the rate of non-smokers = epidemiological evidence.
In the period 1918 to 1919, it has been estimated that 20-40 million people died in the Great Flu Pandemic around the world. The estimate for the United States alone is that 675,000 died. The latest flu strains have been very virulent. Thank goodness so many people in the U.S.A. have taken the shots or the death rates would be much higher nowadays.
When I work in China, Nepal, India or Africa, I read about the huge number of flu related deaths. When I am home, I run to get the latest flu shot.
Ron