mRNA Vaccines
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How do mRNA vaccines work?
Most traditional vaccines, such as those for the flu, contain an infectious pathogen or a part of it, but mRNA vaccines deliver the genetic instructions for our cells to make viral or bacterial proteins themselves. Our immune system responds to these and builds up immunity. Firstly what is messenger RNA also written mRNA? It is a single-stranded molecule naturally present in all of our cells. It carries the instructions from the nucleus to the cytoplasm and had the directions for making a protein. These directions come from the genes on our DNA. But DNA can't leave the nucleus to make proteins so mRNA helps. ribosomal RNA, rRNA and transfer RNA, tRNA in the cytoplasm then translate the information stored in mRNA and make proteins in a biological process called translation.
An mRNA vaccine delivers the instructions for making a bacterial or viral protein to our cells. This cuts out the gene needing to be on our DNA because the vaccine provides the instructions to the cell without using your DNA. Our immune system then responds to these proteins and develops the tools to react to future infections with the pathogen. mRNA vaccine technology is not new, but there were no mRNA vaccines that had approval for use in humans until recently.
What is different about mRNA vaccines?
Some vaccines use a whole virus or bacterium to teach our bodies how to build up immunity to the pathogen. These pathogens are inactivated, which means weakened. Other vaccines use parts of viruses or bacteria, this is known as recombinant vaccine technology and it employs yeast or bacterial cells to made many copies of a particular viral or bacterial protein or sometimes a small part of the protein. mRNA vaccines bypass this step. They are chemically synthesized without the need for cells or pathogens, making the production process simpler. mRNA vaccines carry the information that allows our own cells to make the pathogen’s proteins or protein fragments themselves. Importantly, mRNA vaccines only carry the information to make a small part of a pathogen. From this information, it is not possible for our cells to make the whole pathogen thus mitigating the possibility of infection. The mRNA COVID-19 vaccines that Pfizer/BioNTech, Johnson and Johnson and Moderna have developed cannot cause COVID-19. They do not carry the full information for our cells to make the SARS-CoV-2 virus, and therefore, cannot cause an infection. Of course this seems so simple but the technology is very sophisticated.
Addressing stability and safety
mRNA is a fragile molecule, if you could see it it would look like 1/2 a DNA strand. Delivering mRNA successfully to cells inside our bodies and ensuring that enzymes within our cells do not harm or change it are key challenges in mRNA vaccine development. Chemical modifications during the manufacturing process can significantly improve the stability of mRNA vaccines. Encapsulating, or covering the mRNA in lipid nanoparticles is one way to ensure that a vaccine can successfully enter cells and deliver the mRNA into the cytoplasm. mRNA does not linger in our cells for long. Once it has passed its instructions to the protein-making machinery in our cells, enzymes called ribonucleases (RNases) break down the mRNA.
It is not possible for mRNA to move into the nucleus of a cell as it lacks the signals that would allow it to enter this compartment. This means that RNA cannot integrate into the DNA of the vaccinated cell. If this could happen it would be changing or mutating the DNA of the vaccine recipient and this would be catastrophic for the recieving person. There is no risk of long-term genetic changes with mRNA vaccines. The mRNA COVID-19 vaccines that are currently on the market have undergone safety testing in human clinical trials. For example, the United States Food and Drug Administration (FDA) have granted Emergency Use Authorization for the Pfizer mRNA vaccine after reviewing the safety data from over 37,000 trial participants.
the FDA reports that:
The most commonly reported side effects, which typically lasted several days, were pain at the injection site, tiredness, headache, muscle pain, chills, joint pain, and fever.
Of note, more people experienced these side effects after the second dose than after the first dose, so it is important for vaccination providers and recipients to expect that there may be some side effects after either dose, but even more so after the second dose.
Just in case you are curious here are what the three types of RNA listed in the article look like, and how they function...
* Modified from https://www.medicalnewstoday.com/articles/how-do-mrna-vaccines-work#Addressing-stability-and-safety .
