(CNN) President Donald Trump claimed Friday there will be enough coronavirus vaccines for every American by April -- a claim that doesn't match any timeline given by the federal government's health agencies, private researchers or even the companies making the vaccines.
But Trump and one of his top advisers said they were confident that a vaccine would be approved, manufactured and ready for distribution to all by April.
"As soon as a vaccine is approved the administration will deliver it to the American people immediately," Trump said at a White House news briefing on Friday. "Distribution will begin with 24 hours after notice."
The federal government's Operation Warp Speed program for developing a vaccine earlier this week made the same promise. But Trump went further.
"We'll have manufactured at least 100 million vaccine doses before the end of the year, and likely much more than that," he said. "Millions of doses will be available every month, and we expect to have enough vaccines for every American by April."
The companies working to develop coronavirus vaccines have already started manufacturing doses, even while they are still testing the vaccines to ensure they are safe and to see whether they protect people from infection. They will have to take any data showing this safety and efficacy to the US Food and Drug Administration, and request either emergency use authorization of full approval. The FDA will then decide whether to grant the go-ahead.
Distribution is likely to be complicated and time consuming as well, experts have told CNN.
But Trump's newest adviser on the White House Coronavirus Task Force, Dr. Scott Atlas, echoed the April promise at the news briefing.
"By April every single American who wants to be vaccinated will have the ability to be vaccinated," Atlas said.
Earlier this week, Centers for Disease Control and Prevention director Dr. Robert Redfield told a Senate Appropriations committee hearing that it would likely be the second or third quarter of next year -- late spring or summer -- before widespread vaccination could be underway in the US.
National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci has said he agrees with that timeline.
Asked about that, Trump responded: "That's on the outer edge, we think we can beat that number very substantially."
After Trump's news conference, an administration health official told CNN much depends on the vaccine development process which is still underway. "Are they going to be safe and effective?" the official asked.
The official said Americans may still not be able to get back to normal life until the third or fourth quarter of next year.
Dr. Peter Hotez, a pediatrician, vaccine expert and dean of the National School of Tropical Medicine at the Baylor College of Medicine, told CNN that Trump's promise is unrealistic.
"There's too many unknowns right now for either the President or Dr. Atlas to make those statements," Hotez said.
"First of all, we don't even know if any of the three Operation Warp Speed vaccines in clinical trials even work or if they are safe," he added.
"And we are manufacturing at risk, so I believe the manufacturing numbers are possible but then depending on which vaccine of the three works, or all three works, we don't even have details on the distribution."
Most groups advising the federal government on a vaccine distribution plan have advised immunizing people in groups, with frontline health care workers and people at high risk of severe illness at the front of the line.
"Can we vaccinate all of the country by April? I don't see how that's possible," Hotez said.
"To have the nation vaccinated by the end of 2021 would still be a world land speed record."