Novavax shares jumped more than 15% on Monday after the company secured a long-awaited U.S. regulatory approval for its COVID-19 vaccine, albeit with new conditions, which helped allay some investor concerns over the future of the shot.

Novavax originally showed its vaccine was safe and effective in a 30,000-person clinical trial. The FDA had been on track to grant Novavax full approval – without restrictions -- by its April 1 target date, according to two people with direct knowledge of the situation who spoke on condition of anonymity to discuss confidential agency matters.

The U.S. Food and Drug Administration approved Novavax's COVIDd-19 vaccine with age restrictions after a six-week delay.