3. Production Process

The first step in vaccine development is to grow a modified version of the microorganism that causes the disease. It is modified so that the immune system can still recognize it, but so that it no longer causes harm. There are three main types of vaccine: live-attenuated, inactivated and sub-unit.

Live-attenuated vaccines are made from live microorganisms that have been modified to weaken them so that they do not cause disease. These types of vaccine are very good activators of the immune response because they are very similar to the natural infection. They may not, however, be appropriate for people with a weakened immune system (e.g. individuals with human immunodeficiency virus (HIV) or those who are receiving chemotherapy). Another disadvantage is that the vaccines need to be kept cool and therefore may not be suitable if no refrigeration is available.

Alternatively, vaccines can contain viruses or bacteria that have been inactivated using chemicals, radiation or heat. These are known as inactivated vaccines. These are more stable than live-attenuated vaccines and do not require refrigeration, so can be distributed more easily; however, they are not quite as effective at stimulating the immune system as live-attenuated vaccines, so repeat vaccinations (boosters) may be required after a few years.

Sub-unit vaccines contain selected antigens from a microorganism that are able to provoke an immune response. A fourth, but less common, type of vaccine is made from the toxins produced by microorganisms, rather than parts of the microorganism itself.

As of the start of 2014, a number of new approaches to vaccination are being researched. These included the use of DNA vaccines. Individuals are vaccinated with DNA containing the genetic codes needed to make antigens from scratch. The body’s own cells then secrete the antigens and the immune system responds to them in the same way as it would react to a conventional vaccine. Another method under development in 2014 is the use of vector vaccines. In these cases, harmless viruses or bacteria are used as carriers to transport the DNA encoding the antigens of disease-causing microorganisms. These vectors mimic an infection, but because they are harmless, they do not cause disease. The antigens are still displayed, however, allowing the immune system to learn to recognise them.

Many vaccines contain additional ingredients. Aluminium-based adjuvants are often added to enhance the immune response, thereby making vaccines more effective. They work by helping the immune system to see the antigens in the vaccine. This reduces the amount of microorganism or antigen needed, and may reduce the number of repeat vaccinations required, thereby reducing the cost. Vaccines also often contain stabilisers or preservatives to prolong their lifespan and improve their storage.

As with other medicines, vaccines must be tested in clinical trials to demonstrate that they are effective and to assess side effects. This process generally takes several years, but can be even longer for vaccines as they are generally not used to treat patients, but are tested in healthy people who are at particular risk of infection.