The production of a vaccine can be divided in the following steps:
1. Generation of the antigen
The first step in order to produce a vaccine is generating the antigen that will trigger the immune response. For this purpose the pathogen’s proteins or DNA need to be grown and harvested using the following mechanisms:
- Viruses are grown on primary cells such as cells from chicken embryos or using fertilised eggs (e.g. influenza vaccine) or cell lines that reproduce repeatedly (e.g. hepatitis A)
- Bacteria are grown in bioreactors which are devices that use a particular growth medium that optimises the production of the antigens
- Recombinant proteins derived from the pathogen can be generated either in yeast, bacteria or cell cultures.
2. Release and isolation of the antigen
The aim of this second step is to release as much virus or bacteria as possible. To achieve this, the antigen will be separated from the cells and isolated from the proteins and other parts of the growth medium that are still present.
In a third step the antigen will need to be purified in order to produce a high purity/quality product.
This will be accomplished using different techniques for protein purification. For this purpose several separation steps will be carried out using the differences in for instance protein size, physico-chemical properties, binding affinity or biological activity.
4. Addition of other components
The fourth step may include the addition of an adjuvant, which is a material that enhances the recipient’s immune response to a supplied antigen. The vaccine is then formulated by adding stabilizers to prolong the storage life or preservatives to allow multi-dose vials to be used safely as needed. Due to potential incompatibilities and interactions between antigens and other ingredients, combination vaccines will be more challenging to develop. Finally, all components that constitute the final vaccine are combined and mixed uniformly in a single vial or syringe.
Once the vaccine is put in recipient vessel (either a vial or a syringe), it is sealed with sterile stoppers. All the processes described above will have to comply with the standards defined for Good Manufacturing Practices that will involve several quality controls and an adequate infrastructure and separation of activities to avoid cross-contamination, as shown in the diagram below. Finally, the vaccine is labelled and distributed worldwide.