Immunisation is a process by which a person becomes protected against a disease or made immune to an infectious disease through vaccination.
The process of immunisation usually begins in childhood, but it is important to keep up to date with regular vaccinations throughout adult life to make sure a person is protected from infections. Immunisation describes the actual immunological changes that the body go through post-vaccination. Immunisations confers immunity, meaning thereby that a person become immune to a disease when the body is exposed to pathogens (disease causing organisms) and develop antibodies to fight against it.
This means, that the term immunisation infers vaccination rather than natural infection.
Although immunisation is used interchangeably with vaccination or inoculation, but Inoculation is ultimately an act of introducing a vaccine into a person’s body, and vaccination is the process of introducing a vaccine that spurs immunity. Vaccination is a simple, safe and effective way of protecting people against harmful diseases. In either case, it is the introduction of a Vaccine that stimulates the process of immunisation resulting in the development of immunity.
Vaccine is defined as a product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease.
Vaccine reduces the risk of getting a disease by working with body’s natural defence mechanism to build protection. But how does it work?
When a vaccine is introduced into the body, the immune system responds by way of;
- recognising the introduced microorganism (virus or bacteria)
- producing antibodies, which are proteins produced naturally by the immune system
- remembering the disease and how to fight it, such that when a person gets exposed to the pathogen in the future, the immune system in response quickly destroy it before becoming unwell
On receiving a vaccine, the immune system recognizes the substance as harmful and tailor-made antibodies get designed to target that disease, specifically. This is referred to as the acquired or adaptive immunity. Such an immune response not only attacks and neutralizes the specific pathogen but leaves behind memory cells to re-launch an attack should that pathogen return.
The duration of immunity can vary by the vaccine, with some wearing off relatively quickly and others providing durable protection. In cases where immunity has begun to wane, revaccination or booster shots may be needed.
Vaccines are created after considering the following;
- how does the immune system respond to the pathogen
- who needs to be vaccinated against the pathogen
- best available technology or approach to create the vaccine
Based on these consideration different types of vaccine are created, which include;
- Inactivated vaccines: use the killed version of the pathogen. Examples of such vaccines are Rabies and Hepatitis A
- Live-attenuated vaccines: a weakened or attenuated form of a pathogen is used. Examples are MMR, Smallpox, and Chickenpox
- Messenger RNA (mRNA) vaccines: make proteins in order to trigger the immune response. Some of the COVID-19 vaccines are the best example of mRNA vaccine
- Subunit, recombinant, polysaccharide, and conjugate vaccines: use specific pieces of the pathogen like its protein, sugar, or capsid. Examples of such vaccine include Hepatitis B, Pneumococcal, and Meningococcal.
- Toxoid vaccines: are produced by using the toxin made by the pathogen. Best example of toxoid vaccines are that of Diphtheria and Tetanus
- Viral vector vaccines: are produced using viral vector technology, wherein modified version of a virus is used as a vector to deliver protection. Adenovirus as one of the viral vectors have been used one of the COVID-19 vaccine
Other good references for Vaccine and its types: