Have we reached the point where we can speculate about vaccine timelines?
“When will we have a vaccine?” is a question that I get asked on the regular. I think when the pandemic started, this was anybody’s guess, but with several vaccines entering Phase 3 trials, we are nearing the point where we can begin to speculate about the answer.
The first thing we need to understand is the different types of vaccines. The Moderna and Pfizer-BioNTech vaccines are both nucleic acid vaccines; they include an mRNA that codes for critical parts of the virus, hoping to enlist the patient’s own cells to produce these components and create an immune response. This is a relatively untested vaccine design, and so their early results showing strong immune responses are very impressive for the technological concept as a whole — even if we can’t be sure that the immune response seen is protective.
Another vaccine concept is the ChAdOx vaccine. This is being developed jointly by Oxford University and the pharmaceutical company AstraZeneca. It uses a chimpanzee adenovirus — similar to a human upper respiratory virus that causes colds — that has been genetically altered so that it cannot replicate in humans. This virus has also been altered to produce the “spike glycoprotein” (S) of the virus that causes COVID-19. For what it’s worth, the mRNA-based vaccines also target the S protein.
Here’s a video describing human trials for the ChAdOx1 nCoV-19 vaccine:
The ChAdOx vaccine seems most promising to me because it uses a respiratory virus as its vehicle, and thus gives the immune system more of a “rehearsal” for a real infection with SARS-CoV-2, the virus that causes COVID-19. Generally speaking, the closer a vaccine can be to a natural infection without causing disease, the better. This helps to stimulate the most relevant parts of the immune system that will respond to a natural infection, and hopefully creates the most relevant protection.
But, like I said, the Moderna data were impressive. It could be that their design is enough to get the job done. The following figure, from the publication in The New England Journal of Medicine, is very compelling…