Oxford University and AstraZeneca say their COVID-19 vaccine is 70% effective - but could be up to 90% depending on dosage.
Experts have been trialling the jab in different dosages on 27,000 volunteers in the UK, Brazil and South Africa.
No hospitalisations or severe cases of the virus were recorded in those who received the vaccine.
Two different doses were tested - showing efficacy of 90% in one and 62% in the other, for a combined 70% effective rate.
Oxford says they're now preparing to deliver up to three billion doses of the vaccine, and will submit it to authorities for approval immediately.
Professor Sarah Gilbert, Professor of Vaccinology at the University of Oxford, said: ‘The announcement today takes us another step closer to the time when we can use vaccines to bring an end to the devastation caused by SARS-CoV-2.
"We will continue to work to provide the detailed information to regulators."
It follows promising results from two other trials of coronavirus vaccine candidates from Pfizer / BioNTech and Moderna.
