Of all the Covid-19 vaccine candidates making their way through the regulatory process, the two from Pfizer / BioNTech and Moderna are some of the most exciting. In addition to being reported to be 90% or more effective, these vaccines are the first of their kind. Instead of using killed or weakened viruses or viral protein fragments, these vaccines use messenger RNA, or mRNA for short.
Vaccines based on genetic material can make you think. But mRNA vaccines, which have been in the works for nearly three decades, never touch our DNA and, as a result, cannot interfere with human genes. Instead, they just borrow some of our cellular tools before breaking harmlessly. “Injecting RNA into a person does not affect the DNA of a human cell,” Jeffrey Almond, a microbiologist at the University of Oxford, told the BBC.
It is true that our DNA is a precious resource. Each of our cells carries the complete set of instructions for the proteins that keep our bodies functioning, and changing that code can sometimes lead to disease. But that is exactly why it is so well protected.
Our DNA never leaves the nucleus, a membrane-covered protective bubble inside our cells. To make proteins from that code, an enzyme called RNA polymerase decompresses sections of our double-stranded DNA and makes a copy of the single-stranded mRNA. The mRNA is like the sticky note you use to jot down a recipe from a friend’s cookbook; your cookbook belongs to your house, but you can copy its instructions to help prepare dinner.
Acting like the good messenger that it is, this mRNA exits the nucleus to the rest of the cell, where it meets the ribosomes. These are the protein factories of the cell. Ribosomes read the recipe carried by the mRNA, using the tools of the cell to assemble a chain of amino acids that eventually become a protein.
Covid-19 mRNA vaccines take advantage of this integrated cellular system. The injection introduces a microscopic fatty package into our cells, which carries a specially designed mRNA sequence. When that mRNA meets our ribosomes, they use it to cook up a protein that mimics the SARS-CoV-2 virus, specifically part of its peak protein coat. Our ribosome chefs interpret this new mRNA as if it were a recipe generated from our own DNA, but the DNA within the nucleus of the cell remains intact.
When other entities in the cell notice the SARS-CoV-2 spike protein floating around, they see it as a threat. Protein alone cannot harm us; it is not part of a virus that replicates and explodes and destroys our cells to the point of becoming ill. But it is still enough to trick immune cells into thinking they need to develop antibody protection against it, which is how people are protected against developing Covid-19 once they get vaccinated.
MRNA vaccines are exciting because they don’t introduce any truly foreign viral material; they use modified versions of ingredients that are part of a daily cellular process. Scientists have long suspected that this would mean that they would produce fewer side effects than other vaccine platforms. Data from Pfizer / BioNTech and Moderna suggest that while most people have side effects, ranging from fatigue to mild fevers, they are not severe enough to prevent the vaccine from reaching the public.
These types of vaccines also break down in the body in a matter of hours, which can decrease the likelihood of long-term side effects. (One of the reasons mRNA vaccines have taken decades to develop is because scientists had to figure out how to get them to stay intact. long enough in the cells to be used.)
In theory, mRNA vaccines also have the potential to produce other vaccines at lightning speed. As soon as scientists can genetically sequence new pathogens, they can begin to determine the mRNA necessary to build key proteins within them. This means that future vaccines could be produced on the same rapid timeline as the Pfizer / BioNTech and Moderna Covid-19 vaccines.