"Rule 25. Medical personnel exclusively assigned to medical duties must be respected and protected in all circumstances. They lose their protection if they commit, outside their humanitarian function, acts harmful to the enemy.
"As explained below, the equipment of medical personnel with small arms to defend themselves or their patients and the use of such arms for this purpose do not lead to loss of protection. Furthermore, in analogous application of the similar rule applying to medical units, it is not to be considered a hostile act if medical personnel are escorted by military personnel or such personnel are present or if the medical personnel are in possession of small arms and ammunition taken from their patients and not yet handed over to the proper service.
"Rule 29. Medical transports assigned exclusively to medical transportation must be respected and protected in all circumstances. They lose their protection if they are being used, outside their humanitarian function, to commit acts harmful to the enemy."
Not sure about armor, although the general statement seems to be they would only lose their protected status if they commit specific actions.