(AP) - 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 it fairly. He said experience so far with an antiviral drug that has been found to benefit COVID-19 patients has not given him much distribution confidence. Hospital pharmacies have reported problems getting limited supplies.

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

Bright, wearing a protective mask, testified Thursday before the House Energy and Commerce Committee. Aspects of his complaint about early administration handling of the crisis were expected to be backed up by testimony from an executive of a company that manufactures respirator masks.

A federal watchdog agency has found “reasonable grounds” that Bright was removed from his post as head of the Biomedical Advanced Research and Development Authority after sounding the alarm at the Department of Health and Human Services. Bright alleged he became a target of criticism when he urged early efforts to invest in vaccine development and stock up on supplies.

“Our window of opportunity is closing,” Bright said in his prepared testimony.. “If we fail to develop a national coordinated response, based in science, I fear the pandemic will get far worse and be prolonged, causing unprecedented illness and fatalities.”

Bright's testimony follows this week's warning by Dr. Anthony Fauci, the government's top infectious disease expert, that a rushed lifting of store-closing and stay-at-home restrictions could “turn back the clock,” seeding more suffering and death and complicating efforts to get the economy rolling again.

President Donald Trump on Thursday dismissed Bright in a tweet as “a disgruntled employee, not liked or respected by people I spoke to and who, with his attitude, should no longer be working for our government!" It's a sentiment some of the president’s political allies have expressed about Fauci as well.

More than 84,000 people have died in the U.S., representing more than one-fourth of global deaths and the world's highest toll, according to figures compiled by Johns Hopkins University. On the planet more than 4.3 million have been infected and about 298,000 have died.