Both main British projects to develop a vaccine aim to force the body to build defences against the life-threatening Covid-19 virus before actually encountering it.
They do this by introducing the body to something that looks like the virus, initiating an immune response, without actually causing the disease itself.
In particular, they are looking to mimic a distinctive spike-shaped protein on the surface of the coronavirus. They hope this decoy will provoke the body to generate antibodies that would, if needed, destroy the real thing.
One project is at the University of Oxford's Jenner Institute led by Professor Sarah Gilbert, the other is at Imperial College London led by Professor Robin Shattock.
But though the two projects have similar aims, their methods of provoking this antibody response are quite different.
At Oxford, Gilbert's team is effectively trying to adapt a different virus, taken from chimpanzees, to do the job.
At Imperial, Shattock's team plans to inject a harmless genetic recipe from Sars-CoV-2 into the body, so that the body itself generates the spike proteins.
"We are essentially using nucleic acid, RNA, to deliver the code for the surface protein of the virus," Shattock told the BBC.
"And so we deliver that in, essentially, a liquid droplet. The Oxford group are doing something similar but are using a viral particle to deliver their genetic code to the cells following injection."
That viral particle - chimpanzee adenovirus Oxford 1, or ChAdOx1 - has already been studied as a potential vaccine delivery mechanism against another coronavirus, Middle Eastern respiratory syndrome (Mers), which emerged in Saudi Arabia in 2012.
Now it has been repurposed as ChAdOx1 nCoV-19.
A clinical trial will begin today in the UK to test its efficacy.
In the test, 510 healthy adults between the ages of 18 and 55 will be split into five different groups, and will participate in the study for approximately six months, with the option to have an extra follow-up visit at the end of 12 months, in May 2021.
Two groups will receive a single dose of ChAdOx1 nCoV-19, containing 50 billion so-called "viral particles".
Two control groups will instead receive a single dose of the MenACWY vaccine which protects against four strains of the meningococcal bacteria - A, C, W and Y.
None will know what they have been given.
The fifth group, meanwhile, will be given two doses of ChAdOx1 nCoV-19, one at the beginning of the trial and one after four weeks.
The trial has two very simple aims: does the vaccine work, and is it safe, and will accordingly test for cases of Covd-19 after six months as well as monitoring so-called "serious adverse events" or SAEs.
Imperial's study will not begin until June. But according to Matt Hancock, the Health Secretary, who this week announced £22.5 million funding for Imperial, government money would support clinical trials "to assess a sample of several thousand", and for that to be followed by an even larger trial.
Getting to such human trials now is the fruit of dramatically accelerated work.
Chinese scientists unravelled the genetic code of Sars-Cov-2 within weeks of the first cases.
By early February, Shattock's team had already taken this code and folded the instructions for the spike protein into a genetic molecule, called a plasmid, which can replicate itself.
Together, this self-replicating recipe was injected into mice to see if it was safe.
It is the success of such animal tests that has allowed the team to progress to the human trials.
Shattock said it was an advantage to have two teams - Oxford and Imperial - working on different methods.
"Why it's good to have both approaches is that there are many risks of failure along the way."
So by having two approaches we increase the chances of having an effective vaccine in the UK," he explained.
"And both these approaches could have complementary activity, and so they could eventually be combined if we need to have a prime and boost to make an even more effective vaccine for certain populations."