Exercising immediately after receiving a flu vaccine enhances the effectiveness of the vaccine, according to researchers at Iowa State University. In the study, young adults who received the flu vaccine either participated in a mild-to-moderate exercise regimen for 90 minutes immediately after receiving the vaccine, or remained sedentary for 90 minutes.
Participants who exercised immediately after receiving the vaccine showed a greater level of antibody production than students who remained sedentary. Presumably the higher level of antibody production would better protect the participants who exercised against the flu, but apparently that wasn’t specifically tested in this study. (The study has not yet been published in a peer-reviewed journal.)
The mechanism whereby exercise enhances the effectiveness of the flu vaccine isn’t known yet. The study’s lead researcher speculates that by improving blood flow to some tissues, exercise may speed the delivery of the vaccine to the lymph nodes, where most antibody production takes place. But that remains to be tested.
So go ahead and exercise immediately after the flu shot if you want to: it appears to do more good than harm.