efficacy How the Novavax COVID-19 vaccine differs from those already approved in Canada Early findings from U.K. research show the Novavax vaccine appears to be 86 per cent effective against a new variant of the virus first reported in Britain and 60 per cent effective against the variant circulating in South Africa, the company said on Jan. 28. The efficacy against the original strain of virus that causes COVID-19 is thought to be around 89 per cent.