No, flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are currently made in two ways: the vaccine is made either with a) flu viruses that have been ‘inactivated’ (killed) and that therefore are not infectious, or b) using only a single gene from a flu virus (as opposed to the full virus) in order to produce an immune response without causing infection. This is the case for recombinant influenza vaccines.
