Season 2 Finale Question

In the last few minutes of the finale when Daniel and Helen were in D.C. discussing the dirty bomb attack from Iran on the USA, it got me thinking...

Was only the U.S. affected by the attack?

When Juliette exits the silo at the end of season 1, and we see the outside, all the other silos, and that cityscape in the background, did it just affect the U.S. while the rest of the world is fine?

Or do you think, like COVID, it spread to the rest of the world and every country has its own silos? Or maybe it's the result of a nuclear fallout?