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  • Immunize for Immunity

The Biochemistry Behind Vaccines

Written by: Deekshita Behara

First developed in the late 18th century to protect against smallpox, vaccines have been around for centuries as a means of training the immune system to recognize and combat pathogens. Vaccines contain agents which resemble certain disease-inducing microorganisms, including bacterium, toxins, or viruses. White blood cells, including APCs, T-cells, and B-cells, which participate in immune response, learn to recognize and destroy this pathogen, but in low concentrations.

There are four main types of vaccines, grouped by their composition.

Live, attenuated vaccines: These vaccines contain a weakened form of the actual virus and can fight the disease. Since these vaccines are much like the actual disease, they can provide you with a lifetime of protection against a germ, after being given 1 or 2 doses.

Inactivated vaccines: These vaccines contain the killed virus and can fight the disease. These do not provide prolonged immunity, so booster shots must be taken occasionally.

Toxoid vaccines: These vaccines contain a weakened form of a certain toxin and prevent diseases by providing immunity to certain parts of the toxin-producing bacteria.

Subunit vaccines: These vaccines include specific antigens (a toxin that induces an immune response) of the virus, including proteins, sugars, and/or capsids. Because this vaccine focuses on one element of the germ/disease, the immune response becomes very strong.

Regardless of the type of vaccine, the detection and recognition process of the pathogen is the same. The pathogen is introduced into the bloodstream and is captured by an APC (antigen-presenting cell). An APC works by detecting antigens, ingesting and breaking them down, and traveling to lymph nodes (immune cell clusters). At this point, T-cells and B-cells (types of immune response cells) recognize this antigen as “foreign” and become activated.

Some of these B-cells proliferate and become plasma cells, which can secrete antibodies. Antibodies attach themselves to specific antigens which can prevent the antigen from entering a cell or mark the antigen to be destructed. Once the virus is killed, the immune response cells memorize the antigen from the vaccine, and are able to recognize the pathogen in the future.

So why is this entire process important and how does it benefit the immune system? Well, the body’s response to the pathogen will be stronger and faster than the previous encounter. This is known as a secondary response. In addition to having a resistant immune system, secondary responses also produce more antibodies to fight the pathogen and more memory cells to make for easier identification of the pathogen.

Furthermore, vaccines can also work on a community level. This is known as herd immunity. Some people cannot be vaccinated if they are too young, or if their immune systems are too weak. However, if everyone else is vaccinated, then those who cannot be vaccinated will probably not come in contact with the disease. The threshold for herd immunity can start from having just 40% of the population vaccinated, but it is better if 80% to 95% of a population is vaccinated, in order to prevent prolonged outbreaks.


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