The restrictions on Novavax's vaccine could portend changes at the FDA. Commissioner Marty Makary suggested last week that the agency could update its vaccine approval guidelines “in the coming days.”

The U.S. Food and Drug Administration approved Novavax's COVID-19 vaccine, but limited its use to older adults and people over the age of 12 with conditions that put them at risk due to the illness.The vaccine's prospects were thrown into doubt after the FDA missed its April 1 target to approve the shot,