Question: Will you explain the different types of shots?  I know Pfizer and Moderna are based on mRNA, but I also read that the Johnson and Johnson shot is based on an older technology.  Can you explain the different technologies of the different shots that are coming?

Answer: Gavi, the vaccine alliance offers a really informative overview of the four kinds of vaccines in the world: whole virus, protein subunit, nucleic acid, and viral vector. As of 15 January, there are 64 vaccines against COVID in clinical trials. WHO offers a brief summary of each vaccine here, and I’ve provided Gavi’s definition of each vaccine type plus two examples of each type in the chart below (Chart 1).For the sake of time, I will focus on how viral vector vaccines work, since both the Johnson & Johnson and Astra-Zeneca vaccines are of the viral vector type.  Basically, for both J&J and Astra-Zeneca vaccines, scientists take a little piece of genetic material from the SARS-CoV-2 spike protein and add it to a harmless adenovirus that has the ability to enter the cell, but does not have the ability to reproduce (meaning it can’t make you sick).  Your body reacts to the perceived threat by making antibodies to that spike protein. Ultimately, if/when your body encounters the real SARS-CoV-2 threat, your immune system is prepared to respond.  If you’d like more detail, this article from Prevention magazine is an informative, easy read. Meanwhile, this article from the New England Journal of Medicine, Interim Results of a Phase 1–2a Trial of Ad26.COV2.S Covid-19 Vaccine may also be of interest, though it is a less easy read.  

Finally, one exciting element of the Johnson & Johnson vaccine is that they are exploring the effects of both 1-dose and 2-dose regimens in clinical trials.  Unlike the Pfizer and Moderna vaccines, it’s *possible* (not assured) that the J&J vaccine would only require one dose.  That, coupled with less onerous cold storage requirements, means that if/when the J&J vaccine receives FDA and/or WHO authorization, distribution challenges would be greatly minimized.  *As a reminder, you can read more about how mRNA vaccines work in our Q&A of 12/5.

Chart 1. Vaccines Types (definitions from Gavi)