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Novavax electrified investors last night by announcing that its COVID-19 vaccine NVX-CoV2373 showed efficacy of 89.3% in the company’s first analysis of data from a Phase III trial in the U.K., where a variant strain (B.1.1.7) accounted for about half of all positive cases.

However, NVX-CoV2373 achieved only 60% efficacy in a Phase IIb trial in South Africa, where that country’s escape variant of the virus (B.1.351, also known as 20H/501Y.V2) was seen in 90% of cases, Novavax said.

“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,” Stanley C. Erck, Novavax’s president and CEO, said in a statement.