Viruses, including common respiratory viruses like the flu or the common cold, are typically quite sensitive to heat. Microwaves generate heat by emitting microwave radiation that excites water molecules, which in turn generates heat and cooks the food. When it comes to the survival of viruses, the heat generated by a microwave oven is generally sufficient to inactivate or kill them.
If you were to close the door of a microwave oven without turning it on, the interior would not be actively heated, and any viruses present would not be subjected to the microwave radiation. Without the heat generated by the microwave function, it is unlikely that the viruses would survive for an extended period inside the microwave.
However, it's worth noting that viruses can survive on surfaces outside of the microwave. If there are viruses on the surface of the microwave or other objects placed inside, they can potentially remain viable until they are inactivated or eliminated by other means (such as cleaning or disinfection).
To ensure proper hygiene and reduce the risk of viral transmission, it's important to follow recommended cleaning and disinfection practices, particularly for frequently touched surfaces and objects, regardless of whether or not they have been in a microwave oven.