Researchers concluded that the vaccine is between 62 per cent and 90 per cent effective, depending on how and when the two necessary doses of the jab are administered.
Explaining today’s announcement, Professor Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial, said: “These findings show that we have an effective vaccine that will save many lives.
“Excitingly, we’ve found that one of our dosing regimens may be around 90 per cent effective and if this dosing regime is used, more people could be vaccinated with planned vaccine supply.
“Today’s announcement is only possible thanks to the many volunteers in our trial, and the hard-working and talented team of researchers based around the world.”The news means more than 66 million people in the UK could receive the Oxford University vaccine over the next few months - up from the 50 million initially estimated by scientists.
The UK Government has pre-ordered 100 million doses of the jab. Oxford University said there are four million doses ready to use, with the other 90 million still to be delivered.
However, no one will receive the vaccine until it is approved by regulators, tasked with assessing its safety and effectiveness.
If it is approved, care home residents and staff will be first in line to receive the vaccine, followed by NHS workers and the over-85s.
It comes after similar vaccine trials by Pfizer and Moderna reported effectiveness at preventing symptoms of Covid-19 of between 90 per cent and 95 per cent.
However, anything higher than 50 per cent would have been widely considered a triumph at the start of the pandemic.
The Oxford University vaccine is also projected to be much cheaper than its competitors, and far easier to transport and store safely.
Unlike its Pfizer and Moderna counterparts which need to be stored well below freezing, the Oxford University jab can be kept at fridge temperature.
It means it can potentially be transported across the world to help immunise tens of millions of people in less-accessible regions of the globe.