There are missile defenses, but not nearly enough to counter China’s, let alone Russia’s, full arsenal. Superpowers want to have enough weapon’s to overwhelm their adversaries’ missile defenses. The perverse calculation of MAD is that while both can destroy each other, no one attacks. But if one country thinks they can survive a retaliation, suddenly nuclear is on the table.

The only logical (if perverse) reaction to your adversary building missile defenses, is to build more missiles. This is a route to escalation. This has been extensively studied during the cold war, and is no less true now: amacad.org/…/understanding-chinese-and-russian-vi…

And missile defenses are way, way more expensive and technologically burdensome than missiles. So no, I don’t think that Russia nor China have large scale defenses, for now.