|protein. These instructions include only a very limited set of protein-coding instructions compared to the whole viral genome; in this way, they simulate a viral infection without risk of a real infection. They can potentially provoke a robust immune response because by activating two different arms of the immune system, one dealing with antibodies and another dealing with immune cells. These immune cells include “memory” T-cells, which may lead to longer immunity. Traditional antiviral vaccines focus on provoking mostly an antibody response.|
|Why do you need to take two doses?|
|SS: The two-dose schedule is what has been tested in the clinical trials to be effective. It is based on previous vaccines where the first injection primes the immune system for an initial response, while a second boost dose could result in a fast and strong response due to immune memory. However, it is still possible that other dosing schedules also provide an effective response—but they have not yet been rigorously tested.|
Why must these types of vaccines be kept so cold?
|SS: There are two reasons, having to do with the two main components to the vaccine. First, RNA molecules are not very stable, and refrigeration prevents them from quickly degrading. This RNA component is similar for the Pfizer and Moderna vaccines. The difference between the two vaccines is the lipid nanoparticle that contains the RNA. This lipid component is different for the two vaccines, thus the two vaccines require different temperatures for storage.|
|There is also currently one, single-dose vaccine in Stage 3 clinical trials that are expected to wrap up by the end of January. That vaccine takes a different approach, using an Adenovirus. How do Adenovirus vaccines work?|
|Jingyue Ju: Adenovirus vaccines for COVID-19 are DNA-based. This type of vaccine uses non-replicating Adenovirus—strains of common viruses engineered to be harmless to humans—to serve as a vector to transport DNA codes for the coronavirus’ spike protein to the host cell nucleus.|
|Again, the key is, what these vaccines deliver is just that sliver of the viral DNA, so that the vaccine itself doesn’t make you sick. Inside the nucleus, our cells produce mRNA based on the DNA codes. The mRNA is then used as a template to produce the coronavirus protein, which in turn will activate the immune system in order to protect the host from infection by the real virus.|
From the recipients’ perspective, is there any difference between the two approaches?