Dr. Anthony Fauci warned CNN's Jake Tapper that masks and social distancing should continue despite the development of any vaccine, noting that it likely will not be effective for 5 to 10 percent of the population.
Fauci, the director of the National Institute of Allergy and Infectious Diseases, said he has been through political transitions involving six presidencies.
The US may begin offering the vaccine to priority groups at the end of December, Fauci said. It's like passing a baton in a race. "You don't want to stop and then give it to somebody; you want to essentially keep going".
Currently, the US has more cases - upwards of 11.3 million - than all of Europe, which has 11.1 million cases, according to data from Johns Hopkins University and the European Centre for Disease Prevention and Control.
Vaccines candidates must go through independent data and safety monitoring before approval by the U.S. Food and Drug Administration.
"We still have to get through the next month and the month after that before vaccines arrive", Trudeau said Tuesday in Ottawa.
The U.S. leads the world with 11.2 million coronavirus cases and more than 247,000 deaths.
Tapper said, "Just as a public health measure, you think it would be a good idea if your team would be able to work with the Biden/Harris transition team right now, just in terms of what is best for the public health of the American people?" Globally, more than 1.3 million people have died.
"So, if we get the overwhelming majority of people taking the vaccine, and you have on the one hand an effective vaccine, on the other hand, a high degree of uptake of the vaccine, we could start getting things back to relative normal as we get into the second and third quarter of (2021), where people can start thinking about doing things that were too unsafe just months ago", Fauci said. We want to get it approved as quickly as we possibly can.