10/12/2021
Since the first vaccine was developed in 1796 to treat smallpox,1 several different methods have been adopted to help create new vaccines. Thanks to advances in medical technology, there are now a number of different methods that scientists can explore when addressing the challenge of new or existing preventable diseases.2
Starting with the target pathogen (a bacteria or virus), scientists will look to the different vaccine technologies to identify the approach most likely to induce an immune response as well as considering the potential form of the vaccine - from needle injections and nasal sprays to oral doses.3,4,5
Discover the science behind different vaccine platforms to understand more about how researchers approach preventable diseases…
Live-attenuated vaccines
Live-attenuated vaccines contain live pathogens from either a bacteria or a virus that have been "attenuated," or weakened.2 One of the earliest methods adopted, these vaccines are produced by selecting strains of a bacteria or virus that will ensure a robust enough immune response without causing disease.2
Using a live pathogen tends to create a strong and lasting immune response as the immune system reacts as it would when faced with any other virus,2,6 calling in support from ‘killer’ cytotoxic T cells, helper T cells and antibody-producing B cells.7,8,9 This response also allows time for memory cells against the virus to develop,7 so the immune system is likely to remember the pathogen and be better prepared to fight it in the future.
However, live vaccines can be considered unsuitable for people with a weakened or compromised immune system, such as those undergoing other treatments or with an underlying illness, as there is a risk that even the weakened virus could lead to disease.7
Inactivated vaccines
Like live-attenuated vaccines, inactivated vaccines are developed using a live pathogen however this time it is inactivated or killed so that it can no longer replicate.2 This means that when the vaccine is given, the inactivated pathogen is strong enough to create an immune response without causing disease.2 This makes inactivated vaccines much more suitable for those with compromised immune systems.2
However, the absence of a live pathogen means that inactivated vaccines are less likely to create a strong or long-lasting immune response and multiple doses are often needed in order to build-up longer term immunity.6,7
Subunit vaccines
Subunit vaccines are made from components of a pathogen, incapable of causing disease but specifically selected to help stimulate an immune response.10 Examples of subunit vaccines include polysaccharide vaccines, conjugate vaccines, and protein-based vaccines.
Polysaccharide vaccines use chains of sugar molecules (polysaccharides) replicated from the cell walls of the target pathogen, the part of the pathogen which is deemed ‘foreign’ by the immune system.2,10 However, polysaccharide vaccines are not as effective in babies and children.2
When a polysaccharide is attached, or conjugated to something else, a stronger immune response can be generated2 - this is known as a conjugate vaccine. The polysaccharide component is stuck to a protein to help the immune system recognise and respond to the sugar on the bacteria.11
Protein-based vaccines contain isolated proteins from a virus or bacteria, helping the immune system to recognise the pathogen and prepare the body to fight against it.10,12 Some may also contain adjuvants to help further boost the immune response.10
As subunit vaccines only contain pieces of a pathogen, rather than the whole thing, they cannot make you sick or cause infection.10 This makes them more suitable for immunocompromised people where ‘live’ vaccines are not recommended.10
Toxoid vaccines
When attacking the body, some bacteria release poisonous proteins (toxins) that we need to be protected against.2 Toxoid vaccines use an inactivated, harmless version of these toxins to help the body create an immune response to the disease-causing parts of the bacteria or virus, rather than the whole pathogen itself.6,13
Viral vector vaccines
Viral vector vaccines use a harmless virus, different from the virus being targeted, to help deliver instructions to the host’s cells about the antigen the immune system needs to fight.2,14
Once these instructions are received, the cell’s internal machinery will produce a harmless piece of the protein found on the surface of the target pathogen.14 When the cells then display this protein on their own surface, the immune system recognises that the protein doesn’t belong which triggers an immune response, rallying antibodies and other immune cells to fight off the suspected infection.14 Once this process is complete, the body will have learned how to protect itself from future infection from the virus.14
Messenger RNA (mRNA) vaccines
One of the newest areas in vaccine technology is the use of mRNA vaccines, which are developed using the pathogen’s genetic code.15
These vaccines work by introducing into the body a messenger RNA (mRNA) sequence that contains the genetic instructions for the vaccinated person’s own cells to produce the vaccine antigens and generate an immune response.2,15 If a person is ever exposed to that virus again, the body should then be better prepared with the tools (antibodies) needed to fight against it.15
Protecting ourselves and others with vaccination
Regardless of the technology, vaccines remain one of the most important tools in protecting ourselves and our loved ones from illness,16 preventing more serious diseases than any other advance in recent medical history.17
References
WHO. Smallpox vaccines. Last accessed February 2023.
Oxford Vaccine Group. Vaccine Knowledge Project. Types of vaccine. Last accessed February 2023.
Jasmine Tomar, Philip A. Born, Henderik W. Frijlink & Wouter L. J. Hinrichs (2016). Dry influenza vaccines: towards a stable, effective and convenient alternative to conventional parenteral influenza vaccination. Expert Review of Vaccines, 15:11, 1431-1447. Last accessed February 2023.
Birkhoff, M., Leitz, M., & Marx, D. (2009). Advantages of Intranasal Vaccination and Considerations on Device Selection. Indian Journal of Pharmaceutical Sciences, 71(6), 729–731. Last accessed February 2023.
Vela Ramirez, J. E., Sharpe, L. A., & Peppas, N. A. (2017). Current state and challenges in developing oral vaccines. Advanced Drug Delivery Reviews, 114, 116–131. https://doi.org/10.1016/j.addr.2017.04.008. Last accessed February 2023.
Vaccines Europe. Types of vaccines. Last accessed February 2023.
GAVI. What are whole virus vaccines and how could they be used against COVID-19? Last access February 2023.
British Society for Immunology. Helper and Cytotoxic T Cells. Last accessed February 2023.
British Society for Immunology. B Cells. Last accessed February 2023.
GAVI. What are protein subunit vaccines and how could they be used against COVID-19? Last accessed February 2023.
GAVI. Making strides with polysaccharides: life-saving conjugate vaccines, explained. Last accessed February 2023.
Council of the European Union. How protein-based vaccines work against COVID-19. Last accessed February 2023.
CDC. Understanding How Vaccines Work. Last accessed February 2023.
CDC. Understanding Viral Vector COVID-19 Vaccines. Last accessed February 2023.
PHG Foundation. RNA vaccines: an introduction. Accessed February 2023.
WHO. Vaccines and immunisation. Last accessed February 2023.
ABPI. Valuing Vaccines. Last accessed February 2023.