Are planes shielded from damaging radiation from space?

No. Airplanes are not shielded from cosmic radiation. Our atmosphere protects us, but because airliners fly at high altitudes, airline crews do get a little more radiation each year than the average surface dweller. The amount of radiation per cross-country flight is small, so air travelers need not worry.
No. No aircraft, especially commercial aircraft are "hardened" against radiation, mainly because they don't fly high enough to receive substantial radiation from the sun or space. Even the supersonic concorde wasn't specifically protected since the amount of time it spent over 50-60, 000 ft was relatively short.