Top US health expert Dr Anthony Fauci said a Covid-19 vaccine should be available by the end of 2020, but could take up to a year to roll out to millions of Americans.
To get everyone vaccinated in the US by 2020 would be "logistically tough” said Dr Fauci, head of the National Institute of Allergy and Infectious Diseases and an adviser to the past five US presidents.
“There will be tens of millions of doses available by the end of the year," he said at the Bloomberg Equality Summit.
By the end of the first quarter of 2021 he expects hundreds of millions of doses to be available for the nation’s population of 328 million people.
His comments come as US pharmaceutical giant Johnson & Johnson announced it was entering Phase III trials of its single dose vaccine, joining eight other efforts worldwide in the race.
The single dose is a potential game-changer with two other leading vaccine candidates from Pfizer and Moderna requiring two jabs, which makes things logistically more difficult, according to Dr Fauci.
The US is battling one of the deadliest fronts of the pandemic in the world.
On Tuesday, the country surpassed 200,000 Covid-19-related deaths.
Despite this, Dr Fauci said a “return to normal” could be expected by the end of 2021 - if a vaccine is deployed alongside continued public health measures.
“It will be aspirational, but I think it's more towards the middle to the end of  that you could get people vaccinated," he said.
Vaccine trials require a large number of volunteers of all ages, ethnic backgrounds and include people with underlying health conditions to ensure they are safe and effective for all.
Asked whether Covid-19 trials have had adequate representation of minority groups, Dr Fauci said “we are trying as best as we possibly can … but still we have to do much, much, much better with the relative percentage of African Americans that are in the trial.”
He added: “We want to be able to say with confidence that they are safe and effective in all demographic groups.
"You can make an assumption that they are but we want to prove it by getting the equitable representation in the actual phase III trial.”
Dr Fauci emphasised that the vaccine itself would be free because the Federal government has pre-purchased hundreds of millions of doses. But he did not yet know if there would be an administrative fee added by health care providers.
Frontline medical workers and those at highest risk - particularly low-income minority groups - should be the first to have access to the vaccine when it becomes available, he said.