Vaccines are designed to protect the body against pathogens, either bacteria or viruses. The University of Oxford Vaccine Group states that vaccines are used to prevent disease, unlike medications that are used to treat a disease once you have it.

Vaccines play an important role in keeping people healthy. Infections can cause serious and long-term damage to the body. Infections can be deadly, and they can wipe out a large percentage of the population if they spread. Vaccines help prevent the spread of diseases by creating herd immunity.

How the Body Responds to Infection

When a pathogen enters the body, it attacks the cells and begins to multiply. Infection is the term for when the body has been invaded by pathogens. As the pathogens attack, the cause a person to become ill. The body, sensing an attack, fights back.

According to the Centers for Disease Control (CDC), the immune system increased blood flow to the area where the pathogens are present. The red blood cells bring oxygen, and the white blood cells help fight the infection. There are three types of white blood cells involved:

  • Macrophages digest pathogens and dead or dying cells. Macrophages leave behind parts of the pathogen known as antigens. The body recognizes the antigens as harmful and begins producing antibodies to fight them.
  • B-lymphocytes produce antibodies to fight antigens.
  • T-lymphocytes destroy cells in the body that have already been infected with a pathogen.

It usually takes the body a few days to go from identifying a pathogen to building enough defenses of white blood cells to fight and stop the infection. This process leaves behind antigens, which the body recognizes the next time the pathogen enters the body. Because the body recognizes the threat from the previous exposure, it can react quickly to fight the infection and prevent disease.

How Vaccines Fight Pathogens

By injecting someone with the antigens of a pathogen, the body learns to recognize and fight it without developing the disease an infection would cause. According to Public Health, a resource for medical students, professionals, and patients, introducing antigens triggers the immune response, so the body quickly responds when exposed to the pathogen in the future.

Antigens cause the body to produce B-lymphocytes, T-lymphocytes, and antibodies. The next time the pathogen is encountered by the body, it can fight the pathogen without becoming infected and ill.

Herd Immunity

Most pathogens don’t live long outside of the body. They weaken the longer they are outside of a body and lose their ability to reproduce. They require a host, or a body, to live and multiply. If there are no bodies available, the pathogen may die out because it can’t find enough hosts to stay active.

Once enough people have been exposed to and developed antibodies to a pathogen, it becomes less likely the pathogen will find a new, or susceptible host. Herd immunity is the point where enough of the population has antibodies, known as immunity, that it becomes unlikely an infected person would have contact with someone who isn’t already immune.

Herd immunity slows the spread of infection because enough people are immune to the pathogen that it rarely reaches those who are still susceptible.

The number of people who need to be immune varies depending on how infectious a pathogen is. Some pathogens spread more easily than others, so more people need to be immune to stop spreading it.

As an example, if pathogen A spreads easily through the air, anyone who has contact with an infected person has a good chance of getting infected too. If pathogen B is only spread through blood contact and dies within a few hours on surfaces, fewer people are likely to be exposed or infected. It doesn’t matter as much if you’re not immune to pathogen B if your risk for exposure is low. If you don’t come into contact with the pathogen, you won’t get infected.

Because pathogens can cause severe and deadly illnesses, if the pathogen is easily spread, many people would get sick or die before enough of the population has immunity as a group, or herd, to stop the spread.

The more people that are vaccinated, the less likely it is that a pathogen can spread through the pollution and sicken or kill people. Vaccines allow the population to reach herd immunity without so many getting infected and becoming ill or dying.