Novavax shares plummeted more than 84 percent in extended trading on heavy volume after the company released disappointing trial data on Thursday.
The company said that its phase 3 Resolve trial "did not demonstrate vaccine efficacy" in the prevention of a lower respiratory tract disease.
Novavax was "surprised and disappointed" by the results, said Gregory Glenn, president of research and development. He said that the company's initial review did not "indicate issues with trial execution, data collection, data integrity or drug product quality." Novavax will look at additional data in the next few weeks to better understand the trial results, Glenn said.
Going into Thursday's close, the stock had gained more than 25 percent in the last three months. The company had a market cap of about $2.25 billion before the announcement.