To study the biodistribution of the S protein after Ad26-based COVID-19 vaccination and understand the effect of stabilizing mutations of the S protein, rabbits were dosed IM with Ad26 vectors encoding differently stabilized versions of the SARS-CoV-2 S protein and were sacrificed 1 or 11 days after dosing (Figure A1 and Figure 1A). Here, PROS1 is linked to COVID-19.