What makes a vaccine?

Image Credit: Karolina Grabowska vis Pexels

In the age of COVID-19, science communication has become more important than ever.

In light of what President Trump has postulated in terms of injecting disinfectant as a treatment to the virus and that it is World Immunisation Week, we wanted to take this opportunity to discuss what makes a vaccine. 

Vaccines are one of the most, if not the most, important medical technologies available to us today. Not only can they treat and prevent disease, but they provide protection to vulnerable members of the public who are unable to have them through herd immunity.

Vaccines are preparations that are administered in various ways and not always injected, to provide or stimulate immunity against specific surface molecules (antigens), that the immune system targets. These can belong to viruses, bacteria, parasites, or cancerous cells.  This initiates the production of antibodies in the body. Antibodies are produced by certain immune cells and are specific to a particular antigen. They bind these antigens and act as a flag or marker, encouraging the immune system to attack the invader. Unfortunately, although disinfectants can inactivate COVID-19 outside the body, on inert surfaces, injecting them does not confer immunity. In fact, it will most likely kill you. 

Vaccines can be used as prophylactics or therapies, and within these roles, they can provide passive or induce active immunity. Additionally, we will discuss the role adjuvants play in vaccination. Prophylactic vaccines are used to prevent disease and are given to individuals before they are ill. Classic examples are the seasonal flu shot and HPV. On the other hand, therapeutic vaccines are given after a patient is ill, as an attempt to cure them. These are commonly used to treat certain cancers, such as lymphomas, as well as Ebola and rabies. 

Passive Immunisation

Of the vaccines mentioned previously, the Ebola and rabies vaccines provide passive immunity. This means that the individual receiving the vaccine is being provided with antibodies that are already attuned to the specific antigen, meaning the individual is not required to produce any antibodies themselves. Passive immunisation development involves the extraction of antibodies from immune individuals, purifying them and increasing their concentration, then injecting them. This method is also used in the production of snake antivenom. 

Active vaccines

Active immunisation, unsurprisingly, induces an active immune response in the recipient. In the media, there is a lot of uncertainty associated with this type of vaccination, as it involves the injection of “bad” antigens to stimulate an immune response.  However, these vaccine antigens are modified to prevent them from giving you the disease. To clearly explain the different modifications, we have constructed a table.

Type of VaccineWhat it isExample
InactivatedInactivated whole pathogenInfluenza; Polio
AttenuatedLive whole pathogen with deleted/modified virulence (disease causing) genesTB; MMR
ToxoidInactivated pathogen toxinsTetanus, Snake venom
SubunitNon-dangerous parts of the pathogenHPV, Hepatitis B
ConjugatePolysaccharides found on the surface of bacteriaDiphtheria
Heterotypic/JennerianLive animal pathogen equivalent to the human one, which cannot cause disease in humansBCG


Unfortunately, subunit and conjugate vaccines alone are not strong enough to stimulate an effective immune response and are therefore used alongside adjuvants. Adjuvants enhance and direct the adaptive immune response to the vaccine antigens by promoting an influx of water. This allows more immune cells to reach the lymph nodes and activate a stronger immune response. Aluminium is currently the most common adjuvant in vaccines, however, there are many others in clinical trials. This is not a cause for concern, as the aluminium present in the vaccines is at a low concentration and is not easily absorbed by the body, and the benefits definitely outweigh the risk. Adjuvants increase the reactivity of the immune response, unfortunately resulting in occasional inflammation. The vast majority of the time this isn’t serious, and is similar to the red tenderness that often comes with cuts. Nevertheless, adjuvants can prolong and focus the immune response and contribute to immune memory by increasing its longevity.

Vaccines on a population level are priceless. They can confer herd immunity: if enough individuals in a population are vaccinated against a specific pathogen, an infection cannot spread and so the vaccine prevents an outbreak from occurring in the first place. Their altruistic nature means that when you are being vaccinated, you are also protecting those around you. This becomes vital when considering immunocompromised individuals, who would react dangerously to vaccines due to their lack of an effective immune system. If herd immunity is not met, these individuals are at risk of contracting and dying from preventable diseases. Furthermore, these preventable diseases could be eradicated altogether, as was the case with smallpox, which was declared eradicated in 1980, following the development and the worldwide implementation of the smallpox vaccine. This highlights the importance of vaccination programmes. 

Unfortunately, with the rise of fake news, and the spread of misinformation, vaccination programmes are not meeting the herd immunity criteria in many regions. This is seen in the US with the resurgence of measles after its eradication, and the increase in cervical cancer morbidity and mortality in Japan, where HPV vaccination rates have been dropping. We hope that our review on what makes a vaccine will reduce the mystery of vaccines and encourage you to seek medical information from scientifically accredited organisations such as the WHO and NHS. 

Vaccines are our best bet for controlling COVID-19, however, this will not be an instant solution, as vaccines must undergo rigorous trials and testing to ensure their safety and efficacy. 

So, until then, please stay safe, stay smart, stay six feet apart. 

Written by Tara Gamble and Cristina Huguet Suárez, and edited by Ailie McWhinnie.

Leave a Reply

Your email address will not be published. Required fields are marked *