At FDA, full vaccine approval is the gold standard. The agency was on track to sign off on Novavax’s license 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.

Novavax said on Wednesday U.S. regulators asked the company to produce more data on its COVID-19 vaccine if it gets full approval, sending the drugmaker's shares soaring and easing concerns around the future of the shot.

The company says its vaccine is on track for full approval, following delay. Novavax shares soared following the announcement.