The developers - Pfizer and BioNTech - say their vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised. The companies plan to apply for emergency approval to use the vaccine by the end of the month.
A vaccine is regarded as the best way to control the virus. There are around a dozen in the final stages of testing - known as a phase 3 trial - but this is the first to show any results. It uses a completely experimental approach - that involves injecting part of the virus's genetic code - in order to train the immune system.
Two doses, three weeks apart, are needed. The trials - in US, Germany, Brazil, Argentina, South Africa and Turkey - show 90% protection is achieved seven days after the second dose.
Pfizer believes it will be able to supply 50-million doses by the end of this year, and around 1.3bn by the end of 2021.
