What happened

Coronavirus vaccine developer Novavax's (NVAX 2.46%) stock blasted more than 30% higher in after-market trading on Thursday in reaction to good news about its vaccine candidate.

So what

Novavax announced after market hours that its NVx-CoV2373 met its primary endpoint and demonstrated over 89% efficacy in a phase 3 clinical trial in the U.K. Severe, serious, and medically attended adverse events were at low levels.

The biotech also reported encouraging results for a phase 2b study undertaken in South Africa, although the efficacy was lower (60% in the case of HIV-negative participants, who comprised 94% of the study).

Patient receiving a vaccination shot.

Image source: Getty Images.

Crucially, "NVX-CoV2373 is the first vaccine to demonstrate not only high clinical efficacy against COVID-19 but also significant clinical efficacy against both the rapidly emerging U.K. and South Africa variants," CEO Stanley Erck said. Evidence suggests that the two variants are more contagious than earlier ones.

Novavax is currently enrolling participants for a 30,000-strong phase 3 study in Mexico and the U.S. So far, the company has randomized over 16,000 individuals.

Now what

Yes, the coronavirus vaccines currently authorized in the U.S. -- Moderna's mRNA-1273 and Pfizer and BioNTech's BNT162b2 -- have demonstrated higher efficacy than NVx-CoV2373. Still, 89% is extremely high for any vaccine candidate, particularly one that has been developed as fast as this has.

Novavax seems all but certain to win regulatory authorization for NVx-CoV2373.