A vaccine is a type of medical treatment that is made from inactivated or dead disease-causing microbes, such as viruses. There are two ways that a vaccine can be introduced: by injection or as an oral vaccine. An oral vaccine is one that is taken by mouth, instead of being injected directly into the blood. The goal of all vaccines, whether administered by injection or as an oral vaccine, is to trigger the body’s immune system without the person actually having the disease. It is a way of immunizing, or protecting, the body from getting the disease.
The human body has a number of mechanisms to protect itself from getting an infectious disease. We come into contact with disease-causing agents every day, but don’t end up getting the disease itself. This can be due to a number of reasons including the body's physical, chemical and cellular defenses that either prevent the micro-organisms from entering the body or from spreading if they do manage to get in. If foreign cells do manage to enter the body, they are recognized by the immune system and targeted to be destroyed.
Any molecule that is recognized by the body as foreign is referred to as an antigen. White blood cells called lymphocytes are one type of cell found within the immune system. These cells create a type of protein molecule, called an antibody, that acts against a particular antigen. Antigens and antibodies are highly specific to each other, so an antibody is only secreted if the appropriate antigen is encountered within the body.
The first time an antigen is encountered, it takes some time for the antibodies to be produced. It can sometimes take up to several weeks for enough antibodies to be produced to destroy all the antigens. Once the antigen has been encountered, any subsequent times it is in the body, the reaction is much quicker with antibodies being created in greater numbers and much quicker.
This is the basis of vaccines; they introduce an antigen into the body, without endangering the person. As a result of the antigen being encountered within the body, the immune system creates the appropriate antibodies. This means that should the vaccinated individual encounter the disease antigens, the immune response will be immediate, which will not allow the individual to become infected by the disease.
One of the most common examples of an oral vaccine is the vaccine for polio. This vaccine is an example of a live-attenuated vaccine, which means the virus that causes polio is actually living, but it has been altered so that it is less virulent, or able to cause disease. This oral vaccine has been created to produce immunity to all three viruses that cause polio. As this is a live vaccine, it is thought that immunity is for life.