WASHINGTON (NewsNation Now) — U.S. Food and Drug Administration officials received tough questions Friday on how the agency will determine guidelines for approving a vaccine.

Infectious disease experts pushed agency leaders on the process of collecting safety data and how they evaluate vaccine candidates.

FDA staff said they would gather opinions from experts before signing off on any particular treatment.

At least four companies are currently in late stage trials in the U.S.

Dr. James Baker is the director of the Mary H. Weiser Food Allergy Center at the University of Michigan. Dr. Baker was formally the SVP and worldwide Head of the vaccine franchise at Merck. He joined NewsNation to discuss the FDA hearings.

Watch the interview in the player above.