The body is a huge and complex chemical machine in which thousands of different molecules act and react to provide life. In the giant test tube that is our body, some of these molecules are of fundamental importance in the sense that they control the whole mechanism. In particular, a molecule of deoxyribonucleic acid, or DNA.
DNA? RNA? MRNA?
DNA is a molecule located in the nucleus of a cell and consisting of two complementary strands wound on top of each other, consisting of hundreds of millions of nucleic bases (smaller molecules) and containing all the information that allows an organism to function, from its formation in the embryonic state to everyday development and functioning.
DNA consists of millions of nucleic bases. But if we consider only certain sections of DNA consisting of only ten or several thousand nucleic bases, we will get a gene. The gene encodes (chemically) a separate protein. All genes make up DNA.
Each cell has its own copy of DNA, but they don’t work directly with it to produce the proteins it needs to function. To do this, it passes through an intermediate molecule: ribonucleic acid, or RNA.
Therefore, RNA is a copy of a small part of DNA, which serves as a “working copy” for the cell when it wants to synthesize a certain protein.
When a cell needs to send an RNA molecule from the nucleus to the rest of the cell, it’s like sending a genetic message from one part to another: This strand of RNA is called “messenger RNA”, or mRNA. Thus, the nucleus delegates the synthesis of some proteins to another part of the cell using mRNA.
As soon as RNA (or mRNA) is formed, chemical reactions can occur: RNA will synthesize proteins that are useful for the cell or the body, because in the end this is the goal.
To sum up, DNA contains the entire genetic program of the cell. It is present in every cell.
RNA is a working copy of a part of DNA.
mRNA is when this RNA fragment passes through a cell.
To better understand, we can consider DNA as a dictionary explaining how to encode all the functions and proteins necessary for a living being. If DNA is our dictionary, each gene corresponds to an article. As for RNA, think of it as a copy of a page or dictionary entry, and mRNA is when you send a copied page to someone else to use it instead of you.
A brief reminder of how the immune system works in the face of the virus.
A virus is a piece of genetic material (DNA or RNA) protected by a protein that serves as its membrane. The virus cannot reproduce on its own, and for this it needs a host cell.
The first time an organism encounters a virus, it must make antibodies specific to the proteins of that virus. The virus is untouchable until the body finds a suitable antibody, a bit like when you’re looking for a suitable product for a particular pest (you won’t get rid of rats, snails, or the Colorado potato beetle, for example, with the same products).
This whole operation takes time for the body, and the virus can cause a lot of damage during this time of research.
Once the body has created the right antibodies to the virus present, they can attach to the surface of the virus and act as beacons. Lymphocytes (white blood cells) will target the beacons and thus destroy the virus.
If the patient recovers, it means that he has defeated the virus. The immune system stores antibodies so that they are ready for the next encounter with them. That’s why many viral diseases are detected only once: for the first time. The next time the body destroys the virus before it gets sick, and you don’t even realize it, all because of this memory effect of the immune system.
How the vaccine works
Not all vaccines work on the same principle, but this usually involves giving the patient a weakened or inactive version of the virus to train the body. The body will be alert (sometimes with fever and fatigue), but this is normal and without risk: the contents of the injection are harmless.
The idea is to involve the body in creating antibodies against the virus. Thus, when the latter is actually detected, the virus is destroyed just before we get sick.
Some vaccines inject inactivated viruses (microbial particles that are grown in culture and then killed by heat treatment) directly.
In the case of Covid-19, most vaccines work with mRNA, which works somewhat differently.
mRNA Vaccine Case
During virus infection, a strand of genetic material (RNA in the case of SARS-CoV-2) enters the host cell, and it is the host that will take care of the duplication of the virus. Then the virus is released in the body in large quantities.
It should be understood that an infected cell will use the RNA of the virus as if it were its own. The cell doesn’t see the difference. Worse: too busy following the instructions of the virus, the cell forgets about its normal functioning and may die.
What about the mRNA vaccine?
In these vaccines, we do not inject the whole virus, but only a part of the RNA of the virus. This RNA is harmless (does not cause diseases), but it penetrates into cells and causes them to produce proteins.
Then it is these proteins that will become a target for antibodies and the immune system.
Of course, the produced protein must have the same “signature” as the virus itself: thus, an antibody against this protein can be used against a real virus, and this is what a vaccine of this type is designed for.
The goal is always to teach the body to produce the right antibodies, but instead of directly injecting the deactivated form of the virus, you only inject a piece of its RNA. It is the host’s body that will produce the proteins that the immune system needs.
RNA and mRNA are not very stable molecules: they decompose quickly (in a few hours). In the body, RNA is just a working genetic molecule. She is doomed to disappear quickly after her work is done. In the case of a vaccine, on the other hand, the RNA must be stored long enough between production in the laboratory and injection to the patient. This explains why these vaccines need to be kept cold and why the whole logistics is so problematic.: we are talking about extreme cold, sometimes up to -70°C, which is difficult to achieve.
Why vaccinate as many people as possible?
The purpose of the vaccine is to make a person immune to diseases. This should prevent their illness, suffering and consequences that a real virus would leave behind, as well as the transmission of the disease to other people: the involved immune system destroys the virus before it becomes contagious.
If enough people are vaccinated, the virus will stop circulating as soon as it meets a vaccinated person, thereby protecting everyone.
This happens naturally if a sufficiently large part of the population is immunized (naturally or by vaccination). For SARS-CoV-2, this proportion is estimated at 60% of the population. Therefore, it would be enough to vaccinate 2/3 of the population so that the virus would significantly stop circulating. In this case, we have achieved group immunity: the protection of the entire population as a whole is ensured. Vaccination of the remaining 1/3 of people remains useful, because it allows you to protect not only the group, but also individuals in case of new contact with the disease.
Group immunity does not suppress the virus: it only prevents it from circulating easily. Individual immunity helps to suppress the virus at the individual level.
In addition, viruses, like all organisms, develop rapidly. The quickest way to eradicate the disease is to eradicate it before there is a steady evolution, and therefore to be exposed to a new pandemic and look for a new vaccine (as, for example, in the case of influenza).
Therefore, it is now important to vaccinate the entire population quickly.
MRNA is a chain of RNA that is itself equivalent to a piece of DNA. MRNA allows the cell to work without touching the DNA itself, which remains hidden in the cell nucleus. A cell can synthesize certain proteins that it needs with the help of mRNA.
The vaccine uses the mRNA of the virus: the body’s cells will use this mRNA as if it were their own, and synthesize the protein for which this mRNA encodes.
This protein, although produced by the host cell and harmless, remains a protein alien to the human body, and therefore it will target the immune system, which will then have enough time to find an antibody, while if it encounters a real virus, the latter may begin to cause damage during this time.