Is it safe to get a flu shot when asthma is not under control?

Maybe: Probably better to wait until the asthma is under better control. The vaccination can act as a trigger and the immune response to flu may improve off systemic steroids.

Depends: As long as you avoid the nasal live vaccine (forever) there should not be a problem. However, if your asthma instability requires any short burst oral or IV steroids I would not take it until you were past that treatment by at least 3 weeks. Steroids at therapeutic levels can interfere with the vaccine providing you any benefit.