There are currently more than 230 vaccine candidates using a range of methods to activate antibodies and virus-fighting cells to resist infection. Several have either been licensed for use or are awaiting approval, and vaccinations are taking effect in many countries.
In this article, we want to give you some more information as to;
- Types of vaccines and how they work, and
- Definitions
Types of Vaccines:
1. mRNA Vaccine
Used in: BioNTech/Pfizer, Moderna, CureVac
Although some of the first Covid19 vaccines authorised for use take advantage of mRNA technology, its important to note that this is a fairly new method of protecting against infectious diseases (Although it has been studied for decades). In simple terms, most conventional vaccines we attempt to trigger an immune response in your body by introducing a weakened or inactivated form of the disease.
On the other hand, what mRNA vaccines do is that they instruct our cells to make a protein (or a fraction of a protein), which in itself triggers the desired immune response, producing antibodies that protect us from getting infected once the real virus enters our bodies.
The Covid19 virus has what is called a ‘spike protein’. When an mRNA vaccine is given in your upper arm, it contains within it instructions for your cells to produce a piece of this so called spike protein. Now, the cells that have undergone this production have that piece of the Covid19 spike protein displayed on them. The rest of the immune system recognises that this isn’t normal, and begins building a response by creating antibodies – which means that at the end of the process, your body has learned how to protect against future infection.
This is exactly what happens in your immune system when infected naturally, but in a controlled and safe manner, so that your immune system can ‘know’ the virus before it needs to fight against it. The advantage of this technology is that it can be developed using available materials, and the moment sufficient information about what causes the disease is made known, making process standardisation and production scaling a significantly more feasible endeavour.
The potential for mRNA is unprecedented and probably unrealised – from multiple diseases being treated by the same vaccine, to developments in cancer cell targeting. For now, we can see that, with the necessary funding and international cooperation, this technology is playing its part in defeating the pandemic.
2. Adenovirus-Vectored Vaccine
Used in: AstraZeneca/Oxford University, Johnson & Johnson, Gamaleya, CanSino
Adenovirus vaccines, mostly known as Adenovirus-vectored vaccines, are the ones one can say are closest behind their mRNA counterparts. Like mRNA, the idea is to derive the genetic material that introduced SARS-CoV-2 into your cells and use it to instruct your cells to produce the virus proteins.
The difference between the two, lies in how this is done. So, instead of protecting the mRNA in a shell as is what happens in the first vaccines we mentioned, adenovirus vectored vaccines make use of another, harmless virus (the Adenovirus), to ‘trick’ your body into reacting. Then, when it does, genes that encode the production of the Covid19 spike protein are released. So, really, it uses a virus, to deliver the vaccine which in turn acts against another virus (SARS-CoV-2).
So, to recap, whereas in mRNA vaccines, we introduce the genetic code that instructs your cells to create the Covid19 spike protein, in Adenovirus vectored vaccines, we introduce the DNA of an Adenovirus, which, upon entering into your cells, then turns into the mRNA we want that causes your cells to create the spike protein, which also triggers the desired immune response. Naturally, one can ask if any more risk is being created by introducing another virus – this is why the natural genes that instruct the Adenovirus to replicate itself inside you, are removed.
3. Recombinant spike protein Vaccine
Used in: Novavax, Medicago/GSK, ZFSW
From what has already been said, we know what the spike protein is, so now we can ask, what is the recombinant spike protein method being used to create Covid19 vaccines?
This type of vaccine is made using an existing natural cell, outside of the human body, to produce the vaccine. In the example of Hepatitis B, part of its DNA is inserted into that of Yeast cells – which then produce the desired protein from the virus, which is purified and used as an active ingredient in the vaccine.
Now, lets take the spike proteins that we know populate the surface of the SARS-CoV-2 virus, and go through one of the methods being used to deal with them. The gene that instructs cells to create spike proteins is inserted into a different virus, which in the case we’re speaking of, is a Baculovirus. This Baculovirus is then set to infect moth cells. The moth cells produce more spike proteins and form spikes. Now we have a replication of what happens on the surface of the Coronavirus.
The proteins are then harvested from the moth cells and assembled into nanoparticles, which mimic the molecular structure of Covid19, in a manner that they now cannot replicate or even cause Covid19 in the human body. When the vaccine is injected, a substantial amount of these spike nanoparticles are released along with a compound that attracts immune cells in order to induce a stronger reaction from you immune system. Immune cells, specifically antigen-presenting cells, then break apart these spike proteins and display fragments from them on their surface. As we mentioned earlier, this triggers other cells, known as helper T cells, which when activated, call upon more cells to respond to the vaccine. When these helper T cells find what is called a B cell with a compatible surface, they attach to them, activating them, and causing mass production of antibodies that can deal with the spike proteins.
Now, if, as a vaccinated person, you are later exposed to Covid19, your antibodies can deal with them and the virus cannot enter your cells. Another kind of reaction may be that of a killer T cell – in which case the Covid19 infected cells are directly destroyed before they can even have a chance to replicate.
4. Inactivated Cell Vaccine
Used in: Sinopharm I, Sinopharm II, SinoVac, Bharat Biotech
Inactivated cell vaccines do not contain any live virus, so they cannot ‘create’ the disease and help produce a protection against it. One way of creating an inactivated vaccine is to take the virus, and inactivate or kill it through the use of chemicals, heat or radiation. That said, the pathogens still maintain some of their integrity. That means that they can still be recognized by the immune system and evoke an adaptive immune response, as explained in previous methods. Vaccines such as those that deal with the Flu and Polio, use this method.
Development of these vaccines tends to take a longer time than those mentioned up till now (that is why significant emphasis is being made on new methods’ effectiveness and speed). The reason for this is relatively simple – in order to inactivate a virus, you need specialised laboratories in order to grow it, treat it, and subsequently develop it. This modified pathogen cannot replicate itself and cannot cause disease – so it is definitely safe. But this also means that booster doses are often required in order to retain immunity.
Definitions:
RNA (Ribonucleic acid) is an important biological molecule that is present in all biological cells.
DNA (Deoxyribonucleic acid) is the material that carries all the information about how a living thing will look and function.
Protein is present in all living organisms and includes many essential biological compounds such as enzymes, hormones, and antibodies.
Ribosome is a minute particle consisting of RNA and associated proteins that function to synthesize proteins.
Adenovirus represents a group of common viruses that infect the lining of your eyes, airways and lungs, intestines, urinary tract, and nervous system. They are common causes of fever, coughs, sore throats, diarrhea, and pink eye.
Baculovirus is a member of a family of DNA viruses infecting only invertebrate animals. Some have a very specific insect host and may be used in biological pest control.
SARS-CoV-2 is a severe acute respiratory syndrome coronavirus 2) is the virus that causes Covid19.
mRNA is a single-stranded molecule of that corresponds to the genetic sequence of a gene and is read by a ribosome in the process of synthesizing a protein.
Spike Protein is the protruding chain seen in most images to be ‘sticking out’ of the cell
Active Ingredient is the ingredient in a pharmaceutical drug or pesticide that is biologically active
Antigen-Presenting Cells are a group of immune cells that mediate the cellular immune response by processing and presenting antigens
Helper T Cells play a central role in normal immune responses by producing factors that activate virtually all the other immune system cells
Killer T Cell recognises and kills a virus-infected cell, because a virus will not grow within a dead cell
B Cell traps specific invading viruses and bacteria
Written by: Gianluca Vella
A Bird's Eye View 