Yeah, this is really good news. The spike protein was the logical point of attack, and it seems to have paid off. My understanding , though, is that the vaccine they are now testing raises Abs
to the entire spike protein, not just the receptor binding domain (the part that actually binds to human cells), which was another candidate they were considering. I'm not sure what the situation is with vaccines developed by other companies. However, Entos, a Canadian company, is developing a DNA vaccine that is based not on the spike protein, but another portion of the virus.
Some other positives of the news:
- More than 40,000 subjects, incorporating considerable diversity, were enrolled, so the fact that so far no adverse reactions have been reported is encouraging.
- My understanding is that this is non-replicating mRNA, i.e., just the mRNA itself is injected. The idea is that it will be taken up by cells and translated, i.e., synthesize the protein antigen. It's also possible to inject mRNA with additional factors that will result in copying the mRNA (rather like the coronavirus itself), thus amplifying the response. You end up with a lot more mRNA than you injected into the subject, so the possibility of a much more potent response, if needed (but also a greater risk of side effects). It would presumably also negate the necessity of a second dose, as the Pfizer vaccine (and also the Moderna one) requires.
- It's also possible to inject the mRNA with immune cells that present the antigen on their surface to other immune cells, promoting the response. This might be desirable for older people and others at risk with relatively weak immune systems.
The non-replicating mRNA that Pfizer apparently is using means there is room for improved response, if needed. Arcturus, working with Duke and a medical center in Singapore, is developing a self-replicating mRNA vaccine, which they hope can be administered in a single, very low dose. Imperial College also is developing a self-replicating mRNA vaccine. There are also different ways of delivering it, into the skin or muscle, which I believe is what the study is using, injection into the bloodstream or into specific organs, or even a nasal spray. Then there is Symvivo, a Canadian company that inserts its DNA into bacteria, which are consumed by subjects in a drink, with the idea that the DNA will be released in the gut, and taken up by cells there! This is new territory here, no one really knows what the most effective means of delivery will be.