Whistleblower Dr. Rick Bright warned on Thursday that the U.S. lacks a plan to produce and fairly distribute a coronavirus vaccine when it becomes available. The nation could face “the darkest winter in modern history” unless leaders act decisively, he told a congressional panel.

Bright alleges he was ousted from a high-level scientific post after warning the Trump administration to prepare for the pandemic.

Testifying Thursday, Bright said, “We don’t have (a vaccine plan) yet, and it is a significant concern.” Asked if lawmakers should be worried, Bright responded, “absolutely.”

Bright, a vaccine expert who led a biodefense agency in the Department of Health and Human Services, said the country needs a plan to establish a supply chain for producing tens of millions of doses of a vaccine, and then allocating and distributing them fairly. He said experience so far with an antiviral drug that has been found to benefit COVID-19 patients has not given him much confidence about distribution. Hospital pharmacies have reported problems getting limited supplies.

The White House has begun what it calls “Operation Warp Speed” to quickly produce, distribute and administer a vaccine once it becomes available.