More Detail on How mRNA Vaccines Work

These mRNA vaccine candidates are exciting in that they can be rapidly and safely produced but also have thus far demonstrated greater than 94 to 95 percent immunization success. This is a success rate far in excess of other historical vaccines. But let’s look a bit more closely at how they achieve this. 

During vaccination, the lab-generated mRNA template that codes for the spike protein is delivered, in these cases, via injection into a host’s muscle. (It has been proposed that such vaccines could potentially be delivered by other routes such as nasal spray.)⁴ As this mRNA segment is not part of an intact virion, the mRNA template has been encased, in the lab, within a lipid carrier molecule to further assist the mRNA in successfully reaching and crossing the host cell membrane to carry out its function of entering cells of the just-vaccinated host. 

Upon entering the cell’s cytoplasm, the mRNA redirects some of the cell’s protein production machinery (of which ribosomes are the workhorse) to begin producing viral spike proteins. The produced spike proteins are then incorporated into and “displayed” on the host cell’s outer membrane surface.⁵ This mRNA-directed production is, in some ways, similar to actual virus infection where the infecting virus hijacks the cell’s machinery. When a replication-competent virus infects a cell, the viral mRNA introduced contains templates for all of the proteins the virus needs to replicate. Those sequences redirect our cellular production line into making all the different virus particle proteins. A completed virion is then assembled. A viral particle either exits a cell via an established cellular pathway or is released when a dying cell ruptures. However, in this case only one virus component is produced: the spike protein. None of the other 28 proteins in a typical SARS-CoV-2 genome are manufactured, so the virus itself has not been replicated. Therefore, the host cell’s functions are not otherwise disrupted, and the cell does not die during this production process. 

With the newly manufactured spike protein now situated on the outer membrane of the host cell, it is visible to antibody and T-cell systems. This triggers the body to develop an immunological response, just as it would if the real virus were present. Thus, the body’s immune system has now been “immunized” to attack the SARS-CoV-2 virus if it subsequently invades. In addition, the cell breaks down the existing mRNA after it translates its message into the spike protein, meaning that it can continue to function normally and with no long-term changes.^4,5 It is also important to note that while the synthetic mRNA remains in the cell cytoplasm until broken down, it never enters the nucleus of the cell where the cell’s DNA resides.⁵ Therefore, mRNA vaccines cannot introduce any changes into our own genomes.