The coronavirus vaccine developed by the University of Oxford stops 70% of people developing Covid symptoms, a large-scale trial show.
The Oxford researchers have performed the normally decade-long process of developing a vaccine in around 10 months.
“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 [the virus],” said the vaccine’s architect Prof Sarah Gilbert.
It is both a triumph and a disappointment after vaccines by Pfizer and Moderna showed 95% protection.
However, the Oxford jab is far cheaper, and is easier to store and get to every corner of the world than the other and is expected to play a significant role in tackling the pandemic, if it is approved by regulators.
There is also intriguing data that suggests perfecting the dose could increase protection up to 90%.
The UK government has pre-ordered 100 million doses of the Oxford vaccine, enough to immunise 50 million people.
More than 20,000 volunteers were involved, half in the UK, the rest in Brazil.
There were 30 cases of Covid in people who had two doses of the vaccine and 101 cases in people who received a dummy injection.
The researchers said it works out at 70% protection.
When volunteers were given two “high” doses the protection was 62%, but this rose to 90% when people were given a “low” dose followed by a high one. It’s not clear why there is a difference.
The vaccine is a genetically modified common cold virus that used to infect chimpanzees.
It has been altered to stop it causing an infection in people and to carry the blueprints for part of the coronavirus, known as the spike protein.
Once these blueprints are inside the body, they start the producing the coronavirus’ spike protein, which the immune system recognizes as a threat and tries to squash it.
After Pfizer and Moderna both produced vaccines delivering 95% protection from Covid-19, a figure of 70% is relatively disappointing.
However, anything above 50% would have been considered a triumph just a month ago.
This vaccine can also be stored at fridge temperature, which means it can be distributed to every corner of the world, unlike the Pfizer/BioNTech and Moderna vaccines, which need to be stored at much colder temperatures.