Throughout human history, numerous diseases have had the potential to threaten the survival of civilization. Illnesses like smallpox, polio, measles, and influenza have led to numerous deaths across the planet. However, the invention of vaccines has had the power to prevent those diseases from negatively impacting the human body. Instead of focusing on treating the illnesses after they had developed within human bodies, vaccines train the immune system to recognize and destroy the pathogenic threats before they have the time to negatively impact the body. Overall, then, vaccines have become one of the most important developments within the world of medical science.
In order to understand how vaccines work, it is first important to gain an understanding of the immune system. The immune system is the body’s natural defense against the harmful microorganisms that can enter the body. The immune system’s purpose is to recognize those foreign substances and eliminate them from the body. There are two primary systems of immunity that guard the body against these threats: innate immunity and adaptive immunity.
Innate immunity is the body’s first line of defense. The skin acts as a physical barrier to keep most foreign substances from entering the body. Additionally, there are immune cells in the body that recognize the presence of foreign substances and begin to destroy those entering the body. While innate immunity is fast-acting, it is not specific to the body’s threats, and the same reactions occur each time the body encounters the same foreign substance.
Adaptive immunity, on the other hand, is a more specific system in the body. This system develops after an infection occurs in the body. Two types of white blood cells work to protect the body in this stage of the immune system response: B cells and T cells. B cells produce antibodies that recognize the antigens from the pathogen. Additionally, T cells destroy infected cells in the body. After these foreign substances are eliminated, some B cells and T cells remain in the body as memory cells. These cells “remember” the antigens from the pathogenic threats and prepare to respond to them should the pathogen ever again enter the body.
Vaccines take advantage of the memory cells in the immune system. When an individual is vaccinated, the vaccine introduces a harmless form of the pathogen into the body. Because the body’s immune system recognizes these antigens, the body begins to create antibodies as well as memory cells in response to the harmless introduction. Thus, should the individual ever be exposed to the real pathogen, their immune system would recognize it and begin to eliminate it from the body before it can cause illness.
The biological process behind vaccines involves the body’s immune system recognizing antigens from the vaccine. These antigens activate helper T cells in the body. These activated T cells make B cells recognize the antigens and initiate the B cells to mature into plasma cells. These plasma cells begin to produce antibodies in response to the antigens from the vaccine. In addition, memory cells are created in response as well. These cells remain in the body to protect it in the case that the antigen ever returns.
There are various types of vaccines that have been developed over time. One of the first types is known as the live-attenuated vaccine. These vaccines contain weakened forms of the pathogenic germ. Because it is still alive, the body responds to it as if the pathogen were entering the body normally. These vaccines produce immunity to the pathogen and are used in vaccines for illnesses like measles, mumps, and chickenpox. However, because it contains the living virus, these vaccines are not recommended for individuals whose immune systems may be weakened.
In contrast, inactivated vaccines use killed forms of the pathogen. These vaccines are safe to use for those with weakened immune systems. Examples of inactivated vaccines include influenza vaccines and the polio vaccine created by Jonas Salk. However, the body may not create as strong of an immune response with these vaccines, so boosters may be required.
Subunit vaccines are vaccines that contain only the specific parts of the pathogenic germ. For instance, vaccines may include only the proteins that are found on the pathogen. Only these specific antigens are needed to activate the immune system. Because of this, the body is less likely to experience side effects with these types of vaccines. An example of a subunit vaccine would be the hepatitis B vaccine or the human papillomavirus (HPV) vaccine.
Another type of vaccine that has only recently been developed is the viral vector vaccine and the mRNA vaccine. Viral vector vaccines use another harmless virus to deliver the genetic information that will instruct the body’s cells to produce the protein that is associated with the specific pathogen. This strategy triggers the body’s immune system to recognize the protein as foreign and initiate the immune response. Such vaccines were produced by companies like AstraZeneca and Johnson & Johnson for use during the COVID-19 pandemic.
mRNA vaccines contain the messenger RNA that will instruct the cells in the body to produce the harmless protein from the pathogen. The immune system then recognizes the protein and activates the body’s response to the protein. These vaccines, produced by manufacturers like Pfizer and Moderna, were used during the COVID-19 pandemic. Unlike traditional vaccines, however, mRNA vaccines do not interact with the human DNA; the mRNA molecules do not enter the nucleus of the human cells and do not last past the period in which they are needed for the immune system.
Another critical concept related to vaccines is that of herd immunity. Herd immunity is achieved when a significant portion of the population in a specific area becomes immune to a pathogen. As a result, the spread of that pathogen is greatly limited throughout that population. Even those who are unable to take the vaccines become protected from the pathogen due to the immunity of the majority of the population. Herd immunity has been essential in controlling the spread of numerous diseases around the world, leading to the eradication of smallpox, for instance.
Vaccines have been successful in reducing the number of illnesses that plague the human population. However, there are also some challenges to vaccine use. For instance, the rate at which some viruses mutate prevents the effectiveness of many vaccines from lasting long-term. Herpes and influenza viruses, for instance, are among those that change rapidly. Additionally, as with any medical product, some individuals may be hesitant of using these vaccines. However, vaccines have been tested for safety and effectiveness prior to their release into the population. While some individuals may experience mild side effects after receiving a vaccine, the risks of the illness are much greater than the risks of vaccination.
Overall, then, vaccines work to train the immune system to recognize foreign substances and to destroy them prior to they can create severe illness. The use of memory cells, B cells, T cells, and the immune system’s response to antigens allows for the body to provide protection from numerous illnesses. From the production of live-attenuated vaccines to the most up to date mRNA vaccines, the advancements in the development of these vaccines indicate the development of medicine as an essential science. Thus, as scientists produce new advancements in the production of vaccines, vaccines will continue to be one of the greatest tools in the world for protecting humanity from illness and disease.
World Health Organization. “Vaccines and Immunization: What Is Vaccination?” World Health Organization, 23 Apr. 2024, www.who.int/news-room/questions-and-answers/item/vaccines-and-immunization-what-is-vaccination.
John Hopkins Medicine. “Vaccines.” Www.hopkinsmedicine.org, 14 Feb. 2024, www.hopkinsmedicine.org/health/treatment-tests-and-therapies/vaccines.
“Vaccine Types.” U.S. Department of Health and Human Services, 22 Dec. 2022, www.hhs.gov/immunization/basics/types/index.html.