The regulator said a formal plan for the clinical trial is expected to be finalized this month DUBAI: The US Food and Drug Administration (FDA) has ordered Pfizer Inc. to test the effects of an additional course of its antiviral Paxlovid among people who experience a rebound in COVID-19 after treatment, the regulator said on Friday. The drugmaker must produce initial results of a randomized controlled trial of a second course of the antiviral by Sept. 30 next year, the FDA told Pfizer in a letter dated Aug. 5. The regulator said a formal plan for the clinical trial is expected to be finalized this month. Pfizer is “working with the FDA to finalize a protocol to study patients who may be in need of retreatment,” and will provide details when available, a company spokesperson said.