This work examines the weak stratospheric polar vortex (SPV) event of February 2008 and the strong SPV event of February 2021 to understand the potential influence of SPV strength on midlatitude thermospheric composition and ionospheric plasma density. The weak SPV event shows a reduction in thermospheric O/N2 at all longitudes, changes in the ionospheric total electron content (TEC) that vary with longitude, and an intensification of the semidiurnal tides. The strong SPV event shows O/N2 elevated by up to 25% in the Asian sector and a 25% decrease in semidiurnal tidal amplitude. The TEC response during the strong SPV event is complex, but shows enhanced TEC in the Asian sector where O/N2 is elevated. These are the first observations of anomalies in the thermospheric composition and ionospheric plasma associated with a strong polar vortex event.