Airplane air is less recirculated than you think. The basic mechanism for pressurizing an airplane involves basically running a scoop at the front of the plane and a valve at the back, with the difference between the two controlling the pressure. This means new air is continuously entering the front of the plane and being exhausted out the back.
Compressed air is bled from the engine compressors (or 2 electric compressors in the case of the 787), cooled down using ram air, and passed into an air cycle machine that uses ram air to get the desired pressure and a slightly low temperature. Then it's mixed with filtered recirculated air (taken below the floor around the center of the cabin). Then it's distributed by zone into the whole cabin, brought up to the desired temperature by injecting hot air from the beginning of the cycle, and delivered by nozzles all along the cabin. And excess cabin air is bled out of the cabin, which maintains the right pressure.
However in the case of the virus, the biggest risk arguably doesn't come from the recirculation but the nearby passengers.
That was my understanding as well. Bleed air from the engine is fed into the cabin to maintain altitude pressure, but itβs constantly leaking out of the aircraft too.
