How does a vaccine help protect the body from a virus?
How does the body normally stop a virus?
The body uses its immune system to protect itself from invading particles such as viruses and bacteria. The goal of the virus or bacteria is to replicate and spread. Viruses and pathogenic (destructive) bacteria hurt the human body during replication and spread. The job of the immune system is to limit hurt to the body by destroying the invading particles. As a military has different units such as the air force, army, navy, etc., the immune system has different units for fighting viruses and bacteria. These units are divided into nonspecific (innate) immunity and specific (adaptive) immunity.
Nonspecific (innate) immunity
The nonspecific part of the immune system uses cells that kill (natural killer cells) and eat (phagocytes) harmful particles such as viruses, bacteria, and fungi. It also has nonspecific defenses such as fever and inflammation. In some severe COVID cases, the harm caused by the nonspecific defenses is worse than the damage caused by the virus itself.
Specific (adaptive) immunity
The specific (adaptive) immune system targets a specific virus, bacteria, etc. One important aspect of the specific (adaptive) immune system is antibodies. Antibodies are units produced by cells to stop viruses from entering human cells. They make the virus unable to infect (neutralize the virus). Cells that produce antibodies are called B lymphocytes which mature in the bone marrow. B lymphocytes recognize specific harmful particles. Other components of the specific immune system include T lymphocytes which mature in the thymus gland. T lymphocytes kill or eliminate specific bacteria or virus particles. Each time a new virus, bacteria, etc. is encountered by the human body, the specific (adaptive) immune system takes time to create the specific T or B cells to the invader. As long as a small portion of specific T and B cells still exists in the body, the second time the body encounters the foreign particle, it can much more quickly get rid of it before the virus or bacteria has time to multiple in the body and cause widespread harm.
How does a vaccine help the immune system?
A vaccine primes the specific (adaptive) immune system so that it more quickly sees invading harmful particles. The vaccine can contain a weakened form of the virus, parts of the virus not able to infect, or a blueprint of non-infectious virus parts (mRNA). When the immune system attacks and eliminates the weakened virus, parts of the virus, or non-infectious virus parts created by the body from the blueprint, it learns to recognize and quickly eliminate the dangerous virus capable of inflicting severe disease. A vaccine is analogous to training an army so that it knows how to respond in actual combat. The vaccine trains the immune system how to fight the actual harmful enemy by giving the immune system a less harmful surrogate from which to learn.