The vaccine - called ChAdOx1 nCoV-19 - is being developed at unprecedented speed.
It is made from a genetically engineered virus that causes the common cold in chimpanzees.
It has been heavily modified, first so it cannot cause infections in people and also to make it "look" more like coronavirus.
Scientists did this by transferring the genetic instructions for the coronavirus's "spike protein" - the crucial tool it uses to invade our cells - to the vaccine they were developing.
This means the vaccine resembles the coronavirus and the immune system can learn how to attack it.
James Gallagher “Coronavirus vaccine: First evidence jab can train immune system” https://www.bbc.com/news/health-52677203
“Pfizer and Biontech Announce Early Positive Data from an Ongoing Phase 1.2 Study of MRNA-Based Vaccine Cabdidate against SARS-COV-2” https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-early-positive-data-ongoing-0
*1:See also https://sumita-m.hatenadiary.com/entry/20141004/1412358276 https://sumita-m.hatenadiary.com/entry/20160204/1454598746 https://sumita-m.hatenadiary.com/entry/20160725/1469454984 https://sumita-m.hatenadiary.com/entry/20180425/1524623378
*2:See Pedro M Folegatti, Katie J Ewer, Parvinder K Aley, Brian Angus, Stephan Becker, Sandra Belij-Rammerstorfer, et al. “Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial” https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31604-4/fulltext