British drugs group AstraZeneca and the University of Oxford on Monday said their jointly-developed vaccine against COVID-19 has shown "an average efficacy of 70%" in trials.
"This vaccine's efficacy and safety confirm that it will be highly effective against COVID-19 and will have an immediate impact on this public health emergency," AstraZeneca chief executive Pascal Soriot said in a statement.
The results ranged between 62% and 90% efficacy depending on the vaccine dosage.
The 70% average is lower compared with the efficacy of coronavirus vaccines trialed by rivals Pfizer/BioNTech and Moderna which have come in above 90%.
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Monday's statement said "positive high-level results from an interim analysis of clinical trials of AZD1222 in the UK and Brazil showed the vaccine was highly effective in preventing COVID-19... and no hospitalizations or severe cases of the disease were reported in participants."
It added: "One dosing regimen (n=2,741) showed vaccine efficacy of 90 percent when AZD1222 was given as a half dose, followed by a full dose at least one month apart."
The pair said that regimen n=8,895 showed 62% efficacy when given as two full doses at least one month apart.
"The combined analysis from both dosing regimens (n=11,636) resulted in an average efficacy of 70%."
AstraZeneca said it would "immediately prepare regulatory submission of the data to authorities around the world that have a framework in place for conditional or early approval".
It added that it would seek emergency-use listing from the World Health Organization to accelerate vaccine availability in low-income countries.
AstraZeneca said it is looking at a capacity of up to three billion doses of the vaccine in 2021 pending regulatory approval.
It said the vaccine can be stored, transported and handled "at normal refrigerated conditions" of between two and eight degrees Celsius (36-46 degrees Fahrenheit) for at least six months.
'Save many lives'
More than 23,000 adults are currently being assessed in the trials, with the number expected to rise to up to 60,000, the statement said.
"Clinical trials are also being conducted in the U.S., Japan, Russia, South Africa, Kenya and Latin America with planned trials in other European and Asian countries," it added.
Oxford professor Andrew Pollard said the latest findings show "an effective vaccine that will save many lives".
"Excitingly, we've found that one of our dosing regimens maybe around 90% 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," added Pollard, who is chief investigator of the Oxford Vaccine Trial.
