> The crude incidence of stroke was higher among individuals who had ever received an influenza vaccination (1·25%) compared with those who had not (0·52%; tabl

> The crude incidence of stroke was higher among individuals who had ever received an influenza vaccination (1·25%) compared with those who had not (0·52%; table). However, this crude observation was confounded. Adjusted for age, sex, comorbid illness, and socioeconomic status, recent vaccination (within 182 days) was associated with a reduced hazard of stroke (hazard ratio [HR] 0·775 [95% CI 0·757–0·793]). I doubt that the result of this paper is valid. The crude results have more strokes for people who vaccinated, but they used statistics to demonstrate that vaccination helps. Well there are a lot of choices to make when correcting for factors, and it’s quite hard to evaluate truth that way. The thing which sticks out particularly is correcting for cormorbid conditions. If you do that, you could very well just be pushing out sick people. Two kinds of people will vaccinate more: people who are sick and get encouraged by doctors they see more often, and people who pay more attention to their health. If you “correct for” people with comorbid conditions you might have a larger influence of healthy people who pay attention to their health. In other words, it is plausible that the actual results of the study are “being the sort of person who vaccinates is associated with lower incidence of stroke” not because the vaccine has any effect but because general things people who try to take care of their health do tend to prevent a few strokes (like going to a doctor who notices high blood pressure and getting treatment)