The composition of the 2017-2018 flu shot will be slightly different from last season's flu shot. 1  Specifically, there will be a different strain of the H1N1 virus in this season's flu shot, compared with last season's shot. According to the CDC, the 2017-2018 trivalent flu shot will contain the following strains of the flu virus: 1  A/Michigan/45/2015 (H1N1)pdm09-like virus – This is the H1N1 component that is different from last year's flu shot. 2  A/Hong Kong/4801/2014 (H3N2)-like virus – This is the H3N2 component that is the same as last year's flu shot.