WASHINGTON: US biotech firm Novavax said its Covid-19 vaccine candidate showed 89.3 efficacy in a major phase 3 clinical trial involving more than 15,000 people.

"NVX-CoV2373 has the potential to play an important role in solving this global public health crisis," said the company's president and CEO Stanley Erck.

But the positive news was offset by results that showed it was much less effective against a highly transmissible variant of the coronavirus first identified in South Africa that is spreading quickly around the world.