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Why we need vaccines

The body already has many ways of defending itself against pathogens, which are disease-causing microorganisms. For example, skin, mucus, and cilia all work as physical barriers to prevent pathogens from entering the body in the first place. Pathogens are made up of several subparts, including antigens – the subparts that cause your body to form antibodies. You can consider antibodies to be the soldiers in your body’s defence system; each antibody is trained to recognise one type of antigen. So, why do we need vaccines if our body’s antibodies can just fight off pathogens?

When a new pathogen enters the body, the immune system takes time to recognise and fight it: during this delay, the infection can spread and cause severe illness. Vaccines prepare the immune system in advance, to avoid this delay. Meanwhile, some infections don’t provide lasting immunity, meaning a person can get sick more than once; here, vaccines help boost immunity through multiple shots. Additionally, there is a concept called ‘herd immunity’. When not everyone in a community can get vaccinated (e.g., if some people have weakened immune systems), the disease will have fewer opportunities to spread if enough people do get vaccinated – protecting the entire community.

What are the ingredients in a vaccine?

Antigens are weakened/inactivated (sometimes genetically engineered) pieces of pathogen which train the immune system to recognise and fight the real pathogen by creating antibodies earlier. Antigens could also be small pieces of the actual pathogen, such as a protein or a sugar.

Adjuvants are salts that boost the immune response, helping the body build stronger and longer-lasting protection. Aluminium hydroxide, aluminium phosphate, MF59, and AS01 are all common adjuvants.

Stabilisers prevent chemical reactions from occurring within the vaccine by binding to the vaccine components (like proteins). This protects them from environmental factors like temperature, moisture, pH, and light, preventing the proteins from denaturing and losing their efficacy. Stabilisers can be sugars like lactose and sucrose, amino acids, gelatine, and proteins.

Preservatives are similar in the sense that they keep the vaccine effective, preventing it from becoming contaminated once the vial has been opened (this is handy if the vaccine will be used for more than one person). Preservatives like thimerosal (a form of mercury) or phenol help prevent contamination by killing or inhibiting the growth of bacteria and fungi. They do this by creating an environment that is hostile to harmful microbes: this could be by disrupting the cell membranes or metabolic processes of microbes, maintaining the vaccine’s stable pH, or by acting as antioxidants. This prevents the vaccine components from reacting with oxygen in air, which could lead to chemical breakdown and a weakening of the vaccine.

Surfactants, also known as emulsifiers, keep all the ingredients in the vaccine blended together. They prevent the settling and clumping together of elements that are in the liquid form of the vaccine. They are also often used in foods like ice cream.

Residuals are tiny volumes of various substances used during the making of the vaccine that are not active ingredients. These substances will vary depending on the manufacturing process used and may include egg proteins, yeast, or antibiotics. Agencies like the World Health Organisation place restrictions on the volume of residuals to ensure the vaccine’s safety.

Lastly, diluents are used to dilute the vaccine to the correct concentration, making sure all the ingredients of the vaccine can be delivered safely into the body. The most commonly used diluent is sterile water.

How are vaccines developed?

Developing a vaccine is a long, complex process which typically takes around 10-15 years, but with recent innovations like mRNA technology, this timeline can be accelerated. Once the vaccine has been successfully created in the lab, preclinical testing takes place for about 1-2 years. Here, vaccines are studied in lab cultures and animals to find the proper dosage and potential side effects, and to analyse the immune response. Of course, scientists have to follow strict ethical rules to reduce harm to animals, and alternatives (such as lab-grown human cells) are being developed to reduce the usage of animals. If successful, the vaccine will progress onto clinical trials.