Hi jaap and Ilse,
Many of the most infectious viruses spread through the air. Typically, viruses cannot travel great distances through the air, but many of them can infect people at a distance of several meters from the source.
When people sneeze, cough, or even just while talking (try saying “STay HealTHy”), they create airflows from their mouth and nose. This warm air contains tiny droplets that consist of our respiratory secretions (mucus, slime). Airborne viruses use these droplets to spread from person to person. Once another host inhales the droplets created by an infected person, the virus attaches itself to the cells that line the interior walls of our respiratory tract and infect these cells. From there they can spread from cell to cell within the host.