Could you tell me what happens if you take hepatitis a vaccine twice by accident?

Probably nothing: It should cause no issues but check with your doctor if not feeling well.

U boost immunity: The vaccine is a simple one with no significant problems if taken more than the recommended schedule.It is generally given as a series of 2 doses at least 6 months apart. If you get another later on it would likely just boost your antibody level to hep a.