According to the National Institute of Allergy and Infectious Disease, there are three main types of vaccines. The thing they all have in common is that they intend to elicit an immune response in the host. How they go about triggering the immune response is quite different. Here is a general summary of the three types of vaccines:
- Whole Pathogen Vaccine
The entire structure of the pathogen (which is a harmful virus or bacteria) is introduced to a patient. Your immune system responds accordingly and keeps a memory of the pathogen so when you are exposed again, your immune system already knows what to do to fight the virus. The virus that is exposed may be dead or weakened so it isn’t strong enough to make you sick, but still can elicit an immune response and memory. Common examples include polio (inactivated virus) or measles (weakened virus).
- Subunit Vaccine
As the name implies, these types of vaccines introduce only a part of the virus into the body. Since only a part (or subunit, as it is named) of the pathogen is administered, sometimes a person’s immune response is not robust enough to elicit protection. One way to solve this dampened immune response is to use an adjuvant, which is something that is added to the vaccine to elicit a stronger immune response. Aluminum is a common adjuvant for subunit vaccines, although new adjuvants are a focus of much research. Subunit vaccines are used for many bacteria vaccines to treat infections such as pertussis (whooping cough) and meningitis. One specific type of subunit vaccine is called a recombinant protein vaccine, which is a technology that combines two sections of DNA to create a vaccine. Viral vaccines that use this technology include hepatitis B and HPV (human papillomavirus).
- Nucleic Acid Vaccines
This is the most recently developed type of vaccine technology and its use is first widespread commercial application in humans is the newly developed COVID vaccine. This technology introduces genetic material (nucleic acids) into a person’s healthy cells. This genetic material carries the instructions on how to build the antigen for which an immune response is sought. For example, for the COVID vaccine, the instructions (genetic code) on how to build the S-protein (which is the club-like spike protein on the surface of the virus) is introduced so that a person’s immune system builds a response against the protein that it is actually manufacturing. One example of this type of vaccine is called an mRNA (messenger ribonucleic acid) vaccine. mRNA is a copy of DNA and is used to carry instructions for making proteins to the part of the cell where proteins can be manufactured.mRNA is notoriously unstable but scientists are vigorously researching ways to overcome this, such as encasing the genes in a special coating, for example. Further, sometimes a carrier is needed to transport the genes into a cell. This carrier is called a vector, and vaccines that use this technology are called recombinant vector vaccines, which are commonly used in veterinary vaccines such as rabies.
REFERENCE
National Institute of Allergy and Infectious Disease, Vaccine Types. https://www.niaid.nih.gov/research/vaccine-types.
