The news comes after a study enrolled more than 15,000 participants aged between 18 and 84, including 27% over the age of 65.
According to results from the phase three trial in the UK, the jab also offers 100% protection against severe disease, including all hospital admission and death.
Results show that it is 96% effective in preventing cases caused by the original strain of the coronavirus but 86% effective on combatting the Kent variant.
The UK has already ordered 60million doses of the vaccine, which will be manufactured at the Fujifilm plant in Stockton-on-Tees,
Stanley Erck, president and chief executive officer at Novavax, said: “We are very encouraged by the data showing that NVX-CoV2373 not only provided complete protection against the most severe forms of disease, but also dramatically reduced mild and moderate disease across both trials.
“Importantly, both studies confirmed efficacy against the variant strains.”
In participants 65 years of age and older, 10 cases of Covid-19 were observed, with 90% of those cases occurring in the placebo group.
Novavax expects to use the data to submit for regulatory approval across the world.
Under an in-principle agreement, the UK has secured 60 million doses of the Novavax vaccine.
The UK is providing infrastructure to Novavax in running a phase three clinical trial in the UK, and plans to manufacture its vaccine in the UK with Fujifilm Diosynth Biotechnologies.
In a smaller trial conducted in South Africa – where a more contagious variant is widely circulating, the Novavax vaccine was 55% effective, based on people without HIV but still fully prevented severe illness.
Professor Paul Heath, St George’s, University of London, who is the chief investigator of the UK Novavax vaccine trial said: “These are enormously exciting findings and confirm the results of the earlier interim analysis.
“This is a highly effective and safe Covid-19 vaccine and one that is effective against the important UK variant.
“This wonderful news is a tribute to the over 15,000 volunteers in our trial, to the dedication of the UK investigators and to the huge support of the NIHR.”
Dr Michael Head, senior research fellow in global health, University of Southampton said: “One note of caution is the observed lower effectiveness against B.1.351 variant of concern, as first observed in South Africa.
“This shows the impact variants can have upon the pandemic response and thus is a strong argument for keeping cases as low as possible whilst the burden of Covid-19 is high.
“However, there is still a clear protective effect there in the Novavax trial, and data from across all the Covid-19 vaccines suggests that they will be hugely protective against severe illness from all variants, which is still an excellent outcome.”