Dr. Anthony Fauci, the nation's leading infectious disease expert, spoke about the latest updates on the U.S. vaccine rollout during an interview Monday on ABC News Live.

Fauci, director of the National Institute of Allergy and Infectious Diseases, said that he believes the vaccine will be available to everyone beginning in April, but it won't be until the fall that everyone has actually gotten their shot in the arm.

"It will take several months-May, June, July, August- before you really get what I would consider the herd immunity level, which is an estimate, but I think it's a reasonable estimate, namely getting 70 to 85% of the population vaccinated," Fauci, who is also Biden's chief medical adviser, told ABC News Live.

Fauci said that the timeline is not considering a future approval of coronavirus vaccines developed by Johnson & Johnson and AstraZeneca.

"I think if the J&J or the [AstraZeneca] product comes through with an efficacy that's good enough to be able to be in the mix, that will be very helpful to get things done even sooner than we thought," he said.

Fauci also opened up about an incident where he was exposed to a powder substance that was in his mail last year. The powder was later deemed benign, but only after his security detail put on hazmat suits and sprayed him down.

"It frightened the heck out of my children when they found out about it and my wife too," he said. "I mean, I've decided I'm doing something that might be dangerous but that's it, I chose it. My children did not choose that."

Watch Fauci's full interview with ABC News Live at 7 p.m. and 9 p.m. ET Monday.

The U.S. Federal Emergency Management Agency (FEMA) announced Monday that it would be taking a much bigger role in vaccine rollout going forward.

An inter-agency task force will be established to coordinate the federal response to the country's outbreak. The task force will be "developing data dashboards to track personnel movement and vaccine distribution," according to a statement from FEMA.

The agency previously played a supporting role in running down state needs and managing supply chain issues.

FEMA will also set up federally administered vaccination centers. More details on the centers will be made available in the coming weeks, the agency said.

FEMA also announced it would refund the money states spent to use their National Guard troops to respond to the pandemic.

-ABC News' Matthew Vann

Minnesota health officials announced Monday that they have confirmed the first U.S. case of a new, more contagious variant of the novel coronavirus that initially emerged in Brazil.

The patient, who lives in the Twin Cities metro area, had traveled to Brazil before becoming ill during the first week of January, according to a statement from the Minnesota Department of Health. The specimen was collected Jan. 9.

"With the new lab information showing the case to be the Brazil P.1 variant, MDH epidemiologists are re-interviewing the person to obtain more details about the illness, travel and contacts," the Minnesota Department of Health said in the statement.

Officials warned that "while this variant is thought to be more transmissible than the initial 9 strain of the virus that causes COVID-19 disease, it is not yet known whether the variant causes more severe illness."

-ABC News' Sasha Pezenik

The World Health Organization cited new economic research during a press conference Monday, which warns that vaccine nationalism could cost high-income countries $4.5 trillion. Universal vaccination may make it feel as though life is getting back to normal in wealthy countries, but global trade will suffer if poorer nations still have active COVID-19 transmissions, according to research from the International Chamber of Commerce.

"They will not only feel the hit but bear half the cost," said John W.H. Denton AO, secretary general of the ICC. "If you actually want to fix your own economy you're going to have to get involved in fixing the global economy and part of that is that vaccines flow globally and equitably."

Countries need to focus on the tools we already have to drive down COVID-19 transmissions, according to Dr. Bruce Aylward, adviser to WHO Director General Dr. Tedros Adhanom Ghebreyesus.

"If any country bets everything on the vaccine we're going to lose," Aylward said.

-ABC News' Christine Theodorou contributed to this report.

Forty people in Gambia who tested positive for COVID-19 over the past week have refused to self-isolate or have escaped treatment centers, according to the country's health ministry, which vowed to reveal the identities of those flouting public health regulations.

Officials are also aware of a "large number of travelers who recently arrived" in the small West African nation from countries considered COVID-19 hotspots and "have refused to abide to official protocols and/or report to the health authorities for the mandatory test upon arrival," said Modou Njai, director of health promotion and education at Gambia's Ministry of Health.

"The Ministry continues to treat these matters with utmost and grave concern and thus, the Ministry is hereby giving an order and ultimatum to all those concerned, that they are required to report themselves to the health authorities with immediate effect and failure of which will lead to serious consequences, including the publication of names and identifying information of all those at large," Njai said in a statement Tuesday.

"The Ministry would like to stress that this serious and ruthless misconduct will no longer be condoned under any circumstances," he added. "Anyone found not willing to cooperate with COVID-19 regulations will have their names and identifying information published on the media and thereafter, drastic measures will be taken against anyone that is non-compliant."

Gambia, home to some 2.3 million people, has confirmed 4,008 cases of COVID-19 since the start of the pandemic, including at least 128 deaths, according to the latest data from the health ministry.