Watch: Single-shot vaccine ‘85% effective’
Having a one dose COVID vaccine will dramatically accelerate rollout, not just to the UK, but to the world.
The Johnson & Johnson jab uses similar technology to the AstraZeneca/Oxford vaccine - harnessing a virus to act as a trojan horse that sneaks some of the genetic blueprint for the coronavirus into the body.
But whereas AstraZeneca abandoned hopes of a one-dose vaccine after disappointing results from early clinical trials, the J&J vaccine gets a good immune response with a single injection.
Exactly why isn't clear, but the success matters.
It means people can be protected more quickly. No more disputes over the evidence for delaying a second dose. One will do.
And a single dose also means the same production capacity can protect twice as many people.
Hardly any vaccine has so far reached low and middle income countries so that extra capability is significant.
The price will help too - around Â£7 a shot, roughly the same as two doses of the Oxford vaccine.
We are now seeing the second wave of vaccines, and they are being tested just as new variants emerge around the world.
The J&J jab was tested in Latin America and South Africa - where significant variants have arisen - yet it remained effective.
And the Novavax vaccine got spectacularly good results in the UK, where the Kent variant has swept the nation, and good levels of protection in South Africa too.
Right now we need every dose we can get.
Supply isn't certain for any of the vaccines. They are biological products and we have seen both Pfizer and AstraZeneca struggle to scale up to meet demand.
If the Novavax and J&J vaccines are approved by the UK medical regulator, it would add another 90 million doses to the 157 million that are already on their way.
On the face of it, that is far more than we need.
But some vaccines may be better at preventing disease in the elderly, others may be better at stopping the virus spreading in the young.
And will one vaccine be more effective than the others as a booster next winter against the evolving virus?
At least the UK is now spoilt for choice.
Pick "n" mix is the way forward.
Watch: What UK government support is available?