The Cabal set up agent Keen by infecting her with the virus which could only be spread by touch (unless aerosol-ized and inhaled). That Russian scientist sprayed the virus into Keen's nose, infecting her. Then when she touched Senator Hawkins he was infected, and died.

The part that doesn't make sense to me is this: from the time Keen was infected with the virus until everybody was tested for the virus, Keen must not have touched anyone else who was at the event where Hawkins was infected, except Senator Hawkins. I guess I find it hard to believe that she didn't touch anyone else who was there. That is possible of course, but I would have thought there would have been some incidental contact between her and Ressler or Navabi or someone else who was in that crowd. I thought I saw her grab other people as she was looking for Hawkins. They would have been infected also. Of course no one who was not a close genetic match for Hawkins would be affected by the virus, but they would be infected.

I know, I am being a stickler here. Sometimes these things jump out at me though.