Viruses spread from person to person mainly through the tiny droplets that are produced when a person carrying the virus coughs or sneezes. Those droplets, whether we can see them or not, may fly and land on a surface. Some may land directly on the mouth, nose or eye of another person while others may land on a hard surface like a phone, doorknob or countertop. However, if a virus particle has been brought into your body, it doesn’t guarantee you will get sick. The lungs have cells and mucus lining them that help to trap or get rid of bacteria, particles and viruses. If the virus manages to get past the lungs’ security systems, the protein in the virus must find the perfect cell to bind to, one with the right protein to receive it. The location of the needed receptor plays a major role in whether the host will get sick. Hope that helps