The Cambridge-based pharmaceutical company, said although there was more testing to be done, the results were encouraging and increased “confidence that the vaccine will work”.
AstraZeneca is proceeding with plans to manufacture the vaccine at scale, including 100 million doses for the UK.
Some 1,077 healthy adult volunteers, aged 18-55, are involved in the ongoing phase I/II trial of the vaccine candidate - named AZD1222 - which is being led by Oxford University.
The blinded, multi-centre randomised controlled trial assessed a single dose against a meningococcal conjugate vaccine, called MenACWY, for comparison.
Ten participants also received two doses of AZD1222 one month apart.
The primary purpose of the trials was to show the vaccine was safe, and provoked an immune response.
Interim results, published in The Lancet show a single dose led to a fourfold increase in antibodies to the SARS-CoV-2 virus spike protein in 95 per cent of participants one month after injection. Antibodies are proteins produced by the immune system to neutralise pathogens.
In all participants, a T-cell response was also induced, peaking by day 14, and maintained two months after injection.
T cells are a type of white blood cell that form a key part of the immune system, controlling the body’s response to infection and helping to destroy invaders.