The Company also said it found out that the vaccine was not effective in a smaller study carried out in South Africa due to the presence of the B1.351 variant, the result shows less than 50%.
A mid-stage trial of the vaccine in South Africa, where a troubling new variant of the virus is common, showed 60% effectiveness among people who did not have HIV.
The result from the trial, however, suggest that the vaccine offers protection against the more contagious UK variant of COVID-19.
Novavax shares surged 34% in after-hours trading following the release of the trial results on the same day the United States reported its first cases of the South African variant.
Novavax is already stockpiling vaccine at six operating manufacturing locations and said it expects a total of eight plants in seven countries to produce at the rate of 2 billion doses per year, including from the Serum Institute of India.
The company on a conference call noted that this was interim data and executives said they expect it will be two to three months before they are ready to apply for authorization with regulators.
The UK trial, which enrolled 15,000 people aged 18 to 84, is expected to be used to apply for use in Britain, the European Union and other countries.
Approval of the Novavax vaccine would be most welcome in Europe as it struggles with meagre vaccine supply after Pfizer/BioNTech and AstraZeneca Plc delivered fewer doses than hoped.
Executives on the call said the company was discussing with the U.S. Food and Drug Administration whether the UK and South Africa data was enough to apply for U.S. emergency use authorization.
The UK study took place as the more highly transmissible UK variant was circulating. The preliminary analysis suggests the vaccine was 85.6% effective against this mutation, the U.S. company announced in its news release. It did not provide detailed data.
In the UK trial, the effectiveness of the vaccine was close to that of the two authorized vaccines from Pfizer Inc with BioNTech SE and Moderna Inc, whose two-dose regimens were both around 95% effective at preventing COVID-19 in clinical trials.