LONDON (AFP) -- A coronavirus vaccine developed by drug firm AstraZeneca and Oxford University has shown 70 percent effectiveness in trials involved 23,000 people, they said in a statement on Monday.

The announcement comes after other trials of drugs developed by Pfizer/BioNTech and Moderna announced effectiveness above 90 percent.

The results ranged between 62 and 90 percent efficacy depending on the vaccine dosage, according to Monday's statement.

AstraZeneca chief executive Pascal Soriot said his firm's vaccine would still be highly effective and would have an "immediate impact".

The firm said it would look to develop up to three billion doses of the vaccine in 2021 if it passes the remaining regulatory hurdles.

While the drug showed 90 percent when given as a half-dose followed by a full-dose at least one month apart, the result was 62 percent when given as two full doses over the same time period.

"The combined analysis... resulted in an average efficacy of 70 percent," it said.

It said the vaccine could be stored, transported and handled "at normal refrigerated conditions" of between two and eight degrees Celsius (36 to 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.

Early results suggested there were 131 cases of Covid-19 among the participants but none was serious.

Tests are being carried out also in the United States, Japan, Russia, South Africa, Kenya and Latin America, with trials planned also in other European and Asian countries.

Oxford professor Andrew Pollard said the latest findings suggested the drug was "an effective vaccine that will save many lives".

"Excitingly, we've found that one of our dosing regimens may be around 90 percent effective and if this dosing regime is used, more people could be vaccinated with planned vaccine supply," said Pollard, who is chief investigator of the Oxford Vaccine Trial.

"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."

US biotech giant Pfizer and German partner BioNTech have sought approval to roll out their coronavirus vaccine early, a first step towards relief as surging infections prompt a return to shutdowns that traumatised nations and the global economy earlier this year.

G20 leaders on Sunday said they would "spare no effort" to ensure the fair distribution of coronavirus vaccines worldwide and support poor countries, whose economies have been ravaged by the crisis.

But although the club of the world's richest nations adopted a unified tone, German Chancellor Angela Merkel said she was concerned that no major vaccine agreements had yet been struck for poorer nations.