Human Immunity
People do not get an identical cold twice because our bodies can develop immunity to previously encountered infectious agents, preventing disease progression. Once a person has had an infection, their system learns to fight it and no longer allows pathogens in, or they develop more effective antigens that recognize the infection and defeat it. Unfortunately, people do not always avoid illness.
In contrast, human immunity enables people to survive most infections with few symptoms (Marieb & Smith, 2019). However, if an individual becomes ill for the first time as a result of an infection, particularly if it is a virus that a person has never encountered before, the disease will be far more difficult to treat. Vaccines function similarly, and depending on a person’s level of immunity, they may pass on the disease in a mild form after vaccination or after the illness.
Danger of Viruses
Yet this does not rule out the potential of being infected with the same illnesses. People frequently have viral infections, almost every year. They may not even notice the disease’s symptoms because they are barely noticeable. This is possibly what we mean when we say we never get a cold twice. Furthermore, we are unaware of exactly which virus infected us this time.
In contrast to bacteria, viruses are abundant, making it difficult to determine which one caused our disease. We are only familiar with a few thousand viruses, but there are millions, if not more. As a result, we may encounter an unknown virus at any time, and our immune system will be unprepared for it (Marieb & Smith, 2019). Still, resistance to it develops gradually.
It is also critical to understand the concept of herd immunity. If society has collective immunity to the virus, the individual is more likely to contract the disease or not become ill at all. Therefore, one person’s immunity is insufficient to prevent an epidemic or a pandemic, because colds will persist as long as there are people who lack immunity to this disease.
Reference
Marieb, E. N. & Smith L. A. (2019). Human Anatomy & Physiology Laboratory Manual (13th ed.). Fetal Pig Version.