Vaccines. The hot topic of discussion around the globe. Scientists worldwide have been working day and night to create a solution to the problem we all know too well, the Covid-19 pandemic. This solution comes in the form of the ‘scientific miracle’ we call a vaccine. So, we know that vaccines are here to help in the fight against Covid-19, right? But how exactly do they work?
What does the immune system do?
To understand how vaccines work, we first need to understand a little bit about how the immune system works. The primary job of the immune system is to protect the body from infection, acting as a guard against invading organisms such as bacteria and viruses (like the SARS-CoV-2 coronavirus that causes the disease Covid-19). When an infectious agent first enters our body, our immune system recognises unique proteins on the surface of the virus as foreign and acts to destroy this invader. This initial step takes some time, and so this is when we get sick.
Another way our immune system responds to infection is by producing proteins called antibodies. Antibodies that are specific to the infectious agent act to mark it for destruction by the immune system. These antibodies remain in the body after infection and so, this means that if the body is infected by the same particular infectious agent again, the immune system remembers it and reacts rapidly to destroy it before we get sick 1.
How do Covid-19 vaccines work?
Vaccines are a pretty cool way of manipulating the protective function of the immune system to help us in the fight against Covid-19 and have been described as “one of modern medicine’s greatest success stories 2.
They trick the immune system into thinking we have already been infected with the SARS-CoV-2 virus, triggering SARS-CoV-2-specific antibody production. This means when we do get infected by this virus our immune system is already primed to respond more rapidly and efficiently.
Currently, there are a few different types of Covid-19 vaccines that have been manufactured. These vaccines have been judged in terms of their ‘clinical efficacy’, that is, the percentage of reduction in cases of Covid-19 in the vaccinated group compared to the unvaccinated group 3. Let’s have a shot at understanding how these vaccines work.
Firstly, we have vector vaccines. These vaccines consist of a weakened version of another virus (one that is not SARS-CoV-2) that can induce an immune response but does not cause disease. This virus will be modified so that it contains genetic material from the SARS-CoV-2 virus. Once the virus gets inside our cells, it uses this genetic information to trigger production of a SARS-CoV-2 specific protein. This then induces an immune response. Companies such as AstraZeneca have produced vaccines that work in this way and clinical efficacy looks promising, sitting at about 70% overall.
Next up we have inactivated vaccines. As the name suggests, these vaccines contain an inactivated SARS-CoV-2 virus. This can trigger an immune response without replicating and causing harm. Often this type of vaccine needs a little helper called an ‘adjuvant’ to trigger a strong enough immune response 4. Currently, the Chinese company Sinovac Biotech are trialling this form of vaccine, however, the efficacy rates have been variable in different countries 5.
Vaccines also exist that contain a weakened version of the SARS-CoV-2 virus, rather than a completely inactivated virus. This type is called an attenuated vaccine and tends to trigger a much better immune response than an inactivated vaccine. Currently, no Covid-19 vaccines of this manner have been approved for use; however, the American company Codagenix are in the early stages of trialling this form of vaccine 6. This would have the benefit of being a single-dose vaccine, compared to other available vaccines which require several doses.
Protein vaccines are another form currently being trailed in the fight against Covid-19. This type of vaccine contains the specific proteins from the SARS-CoV-2 virus that antibodies are developed against. As this type of vaccine contains only a small piece of the SARS-CoV-2 virus and not a whole virus, it can also trigger an immune response without causing infection. Again, this type of vaccine sometimes needs a little bit of help from an adjuvant to trigger a strong enough immune response. The American company Novavax announced its vaccine of this format had a high clinical efficacy of 89%.
Last but not least, we have genetic or mRNA vaccines, the type you might have heard being mentioned in the news a lot recently. There’s a lot of hype over this particular type of vaccine because, although research into these vaccines has been ongoing for years, this is the first time they have been approved for use. Before those alarm bells go off in your head, this does not mean it isn’t safe. mRNA vaccines consist of genetic material from the SARS-CoV-2 virus that contains the instructions for our cells to make a SARS-CoV-2 specific protein. Once this is produced, our immune system does its usual job of recognising this protein shouldn’t be in our body and mounts a response against it. Again, because this vaccine only contains genetic material from the SARS-CoV-2 virus, it cannot cause disease 7. Companies such as Pfizer and Moderna have manufactured these vaccines which have been shown to have an efficacy of around 95%. A disadvantage of this type of vaccine is that its components can be quite sensitive to degradation and so it needs to be stored at lower temperatures than usual, the logistics of which can be quite expensive.
A lot of worry is circulating at the minute over the relatively short time taken to approve Covid-19 vaccines, and there are logical reasons for why we were able to get these rolling so quickly! Often, one of the main obstacles in vaccine development is funding. The vigorous safety and efficacy testing involved in vaccine development require huge amounts of money and lack of funding is a common reason for stalling this process. Covid-19 vaccines went through the same safety and efficacy checks as any other vaccine would, but immense amounts of money being pumped into the trials allowed for this financial stalling to be avoided. Another handy thing is the fact that years of research was already available on circulating coronavirus’ such as SARS (severe acute respiratory syndrome) and hence work towards some kind of a vaccine had already started, which provided a pretty useful basis for the creation of other vaccines. This also allowed the vaccine production process to be sped up as a lot of our clever scientists had already done the research 8!
Image credit: Lauren Kelly
Why are there so many different vaccines in development?
We have a few vaccines that have been approved for use, and these have been shown to be very effective, so why do we need to continue pumping money into Covid-19 vaccine development? Well, it’s like any kind of treatment; some Covid-19 vaccines may work for some people and not others, and we need a large variety of vaccines available to work for everyone. Secondly, we need an immense number of vaccines to be rolled out rapidly to get the virus under control and multiple companies working on different vaccines increases the chance of us achieving this goal. Creating multiple vaccines globally also takes the pressure off transporting temperature-sensitive vaccines across long distances. Alternative forms of vaccines that are less sensitive to temperature change would help speed up the roll-out greatly. This would be extremely useful in helping vaccine coverage reach developing countries that also desperately need it 9.
So, there we have it, the world of Covid-19 vaccines. Of course, more research needs to be done to determine how long protection lasts and whether these vaccines prevent viral transmission. However, the fact we have several vaccines available to improve disease outcomes is indeed a ‘medical miracle’ and a jab in the right direction towards controlling this deadly virus.
This article was specialist edited by Anna Kirk and copy-edited by Richard Murchie.
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References
- More information about how vaccines work can be found on the British Society of Immunology’s website here https://www.immunology.org/celebrate-vaccines/public-engagement/guide-childhood-vaccinations/how-vaccines-work
- https://www.who.int/news-room/facts-in-pictures/detail/immunization
- https://www.sciencenews.org/article/coronavirus-what-does-covid-19-vaccine-efficacy-mean
- More information on how different vaccines work can be found here https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.html
- Check out this article here which assesses the different efficacy findings between the different vaccines https://www.biospace.com/article/comparing-covid-19-vaccines-pfizer-biontech-moderna-astrazeneca-oxford-j-and-j-russia-s-sputnik-v/
- For more updates check out the company’s website here https://codagenix.com/
- https://www.immunology.org/coronavirus/connect-coronavirus-public-engagement-resources/types-vaccines-for-covid-19
- https://www.nature.com/articles/d41586-020-03626-1
- For more detail about why it is vital for vaccine development to continue, check out this article here https://wellcome.org/news/four-reasons-why-we-need-multiple-vaccines-covid-19