COVID cannot get through walls that are solid, but instead COVID can spread through doorways and gaps.
Solid materials brick, wood and drywall block the COVID virus and so instead the transmission and spread of COVID goes through gaps, cracks and doorways or ventilation systems.
COVID could be on the wall, but not penetrate through the wall.
To clean the air in your house from COVID, open windows and doors and use fans as well as an air purifier with a HEPA air filter.
Opening doors and windows creates cross ventilation and helps the virus leave the room and allows fresh air in.
Use ceiling fans, exhaust fans or even box fans placed in windows or in the rooms to move air around and push stale air out.
COVID lingers in the air in a room for several hours and even days, and can accumulate and increase in concentration, especially in rooms and areas that are poorly ventilated, which also poses an airborne risk long after an person infected with COVID leaves.
Although the risk of COVID decreases over time and with distance but increases with prolonged exposure and crowdedness.
Poor ventilation in rooms and buildings or homes allows the viral particles to stay longer and good airflow disperses the viral particles faster and smaller and unventilated rooms also hold higher concentrations of the COVID virus.
Also activities that produce more respiratory droplets like exercising, talking, singing etc increase the virus droplets in the air and the longer the space is occupied the higher the risk of COVID.
To help get rid of the virus in the air in the room or building open windows and doors when possible and use air purifiers with HEPA air filters and maintain space from others and wear masks when possible to reduce the release of virus particles and inhalation.
Being outdoors also lessens your risk of catching COVID although even when outside in the fresh air you can still catch COVID, especially if you're around someone that has COVID.
Being outside and in the fresh air lowers your risk of catching COVID significantly because the fresh outdoor air disperses the virus carrying droplets and particles that transmit COVID.
This makes transmission of COVID and other viruses harder than it would be indoors.
However being in close contact with an infected person or people, especially in crowded outdoor settings or for extended periods, still pose a risk of you developing COVID.
So even when outdoors you should try to stay away from people as much as you can and if possible wear a mask.
If you can, having your windows open to allow fresh air in can also help lower the risk of COVID and other viruses as you allow fresh air into the house or room.
This prevents you from breathing in air that could have viruses and germs in the air as much as it would if you kept the windows closed.
Outdoors is also good for when you're sick or have COVID as wind and natural ventilation constantly moves the air and dilutes the COVID virus and other virus concentrations.
And it's also most often easier to maintain physical distance from other people outdoors.
However being in crowds and in close contact with people could increase your risk of getting COVID and other viruses.
High density outdoor events like concerts, busy markets, stores etc increase your chance of close exposure to COVID and other viruses.
And prolonged face to face conversations or activities where you're very near someone infectious also increases your risk of COVID and other infections.