Once a vaccine has been listed for WHO emergency use, the United Nations health agency said, it "engages its regional regulatory networks and partners to inform national health authorities on the vaccine and its anticipated benefits based on data from clinical studies to date".

The WHO's review found that the vaccine met the must-have criteria for safety and efficacy set out by WHO, and that the benefits of using the vaccine to address COVID-19 offset potential risks, the WHO said in a statement.

"This is a very positive step towards ensuring global access to COVID-19 vaccines. But I want to emphasize the need for an even greater global effort to achieve enough vaccine supply to meet the needs of priority populations everywhere," said Dr. Mariangela Simao, WHO assistant-director general for Access to Medicines and Health Products.

The WHO, together with the GAVI Vaccine Alliance and the Coalition for Epidemic Preparedness Innovations, are spearheading a global effort called COVAX to distribute vaccines to low- and middle-income countries, to help make sure that shots do not go only to wealthy nations.

The COVAX alliance has said it has agreements for nearly two billion doses, with first deliveries due in early 2021. The alliance has said it has been in talks with Pfizer and BioNTech to secure vaccine.

Pfizer and BioNTech's messenger RNA vaccine was 95 per cent effective at preventing disease symptoms after two doses 21 days apart. Delivery is challenging, since it needs to be stored at minus 70C.

The vaccine has previously been approved for emergency use in the United States and Britain, and has conditional marketing approval in Europe and Switzerland, among other countries, where distribution of shots concentrating on older people and healthcare workers began in December.

Australian Associated Press