Why are people who have had organ transplants at risk from getting colds?

Answer 1

There is no such thing as a perfect match for organ transplants as everyone has unique antigens (the proteins on cells that say who the cells came from). If the recipient's immune system detects that the donor organ is from someone else it will destroy it and make things even worse for the patient. To avoid this, recipients take immunosupressants which are drugs to decrease the effect the immune response of the recipient can have. The less close a match between the donor and receiver the more stronger the drugs that must be taken. The unfortunate side effect of taking these drugs is that the immune response is less effective at fighting diseases too, so a cold virus finds it much easier to take hold.

Answer 2

People who have had organ transplants are put on medications that supress their immune system. The medications are called immunosupressives, these medications keep your body from attacking the transplanted organ. Your body knows when something new is there and tries to protect itself from the new thing. The new thing can be an organ or a bacteria or a virus. The immune system is what helps you not get sick. If you take a medicine that slows that system down and get exposed to a bacteria or a virus you have a better chance of getting sick