We all get them, but have you ever thought a little about how vaccines are made, what is actually in a vaccine or how they provide you with protection?
In this blog we’ll be covering some of the more general principles about vaccines; the science behind them and how they work. In future blogs, we’ll be addressing specific vaccines and answering some of the more common questions encountered in our practices.
With COVID about, vaccines have been a hot topic and in particular the newer vaccine platforms have been getting significant coverage in the media. In this post we’ll be mainly focusing on the more ‘traditional’ vaccines, such as the ones for travel or those given in childhood. In later blogs I’ll cover some of the newer tech, and more specifically, the COVID vaccines likely to be used in Australia.
‘Traditional’ vaccine technology falls roughly into 4 groups:
- Live attenuated vaccines
- Inactivated vaccines
- Protein and sugar vaccines (polysaccharides and conjugated)
- Adjuvant vaccines
The live attenuated vaccines are viruses (as in the measles/mumps/rubella or chicken pox vaccine) or bacteria (as in the BCG tuberculosis vaccine) that have been made less harmful and infective than it’s ‘wild type’ counterpart. Because these are living vaccines, they are able to induce a good protective response in the body. They can however occasionally cause a weak ‘disease’ pattern experienced as side effects to the vaccine. These side effects are usually mild. Live vaccines are not recommended for those whose immune systems may struggle to fight off infection, for example those on immune suppression medication. They are also not recommended in pregnancy.
Inactivated vaccines are often viruses (as in the hepatitis A vaccine) or bacteria (as in Q fever vaccine) that have been killed and purified to produce a vaccine. They work quite well, but do not produce as strong an immune response as the live vaccines. Vaccines in this group will often need to be given as multiple doses or ‘boosters’ to strengthen the immune protection. The majority of these vaccines can be given to people with immune suppression (with the exception of Q fever).
Polysaccharide based vaccines use sugar molecules found on the outer surface of certain bacteria as the immune system target. While for some vaccines, the sugar alone is enough to to produce an adequate immune response for a specific purpose, they are less effective in children under 2 and the protection is often short lived. Proteins, on the other hand, are potent stimulators of the immune system – but are not always so amenable to vaccine design. To get round this issue, some vaccines, link a polysaccharide (the immune target) to a protein to boost the immune response; these are called conjugated vaccines. An example of this is the HIB (Haemophilus influenzae type b vaccine), which forms a major contributor to the current child immunisation schedule.
The last of the classical vaccine categories include ‘adjuvants.’ As the name suggests another substance is included to ‘help towards’ boosting immunity. The tetanus vaccine is a good example of an adjuvant. Clostridium tetani is a soil bacterium that can contaminate wounds and produce a protein (in this case toxin) paralysing nerves. Fortunately, the structure can be changed just enough so that it doesn’t cause paralysis, but still act as an immune system target. This is called a toxoid. Toxoids can be absorbed onto a carrier particle eg aluminium hydroxide or another protein (such as a whooping cough protein) which then act as the adjuvant. Like the inactivated vaccines, and polysaccharide/conjugate vaccines these will also need to be given multiple times to provide adequate protection.
The other stuff…
When I give vaccines in a clinic, I will often talk about ‘proteins in preservative.’ While this oversimplifies things, it helps to get across the idea that there are other components in vaccines acting to support the ‘active particles’ in some way. Examples of these include emulsifiers – which help everything stay mixed into solution, preservatives – to prolong shelf life and residuals – which are minute amounts of chemicals, proteins or antibiotics left over from the processing stages. Almost all the ‘other stuff’ included in vaccines is used in much larger quantities in the cosmetic, food or pharmaceutical industry.
As you may have read in the media, vaccines and prescribed medications are rigorously studied and tested before they even get to market. When they eventually make their way into widespread use, they continue to be scrutinised to see how good they are, how long they offer protection, and if there are any undesirable effects.
So next time you’re marvelling at the latest device to come out of Silicon Valley, consider the tech involved in developing a humble vaccine; it really is an astonishing piece of human ingenuity.
Dr Kati Davies – YourGP@Denman