(CNN) -- Across the US, preparations are underway to quickly distribute COVID-19 vaccines once authorized, but experts say before that relief occurs, the coming months will be difficult.
What comes next is likely the country's "worst-case scenario in terms of overwhelmed hospitals, in terms of the death count," said emergency medicine physician Dr. Leana Wen.
"There's just so much virus in our communities right now," she said.
Her words echoed a bleak forecast by Centers for Disease Control and Prevention Director Dr. Robert Redfield, who warned Wednesday the next three months are going to be "the most difficult in the public health history of this nation."
It's a grim reality reflected in the latest numbers.
Vaccinations won't have a big impact on deaths by April 1, but universal mask usage could, the IHME team said in a Friday update.
"Scaling up mask use to 95% can save 66,000 lives by April 1," the team said.
Leading health officials say rising cases will be followed by more hospitalizations that could cripple health care systems across the country. Hospitals and experts all over the US are sounding the alarm.
Marvin O'Quinn, president and chief operating officer of CommonSpirit Health, which runs hospitals in 21 states, told CNN that all its hospitals are getting more patients.
"We are now up to roughly 2,100 positive cases in our hospitals. That's an increase of almost 70% since November 11," O'Quinn said. "We're seeing about 70 to 100 new cases every day."
In Pennsylvania, just under 5,000 people are hospitalized with COVID-19, and two parts of the state are inching closer to staffing shortages, Secretary of Health Dr. Rachel Levine said Thursday.
"It is so important to remember that all of us have to be mindful, that we all have a role to play in what is happening in the hospitals right now," Levine said. "You might not need hospital care right now; you might not have a loved one in the hospital right now. But what is happening in our hospitals has a direct impact on you."
"The people who make our health care system work are relying on you to do the right thing," she continued.
And hospitals nationwide have yet to see the impacts that Thanksgiving gatherings and travel could bring, with another surge projected in coming weeks.
On NBC's "Today" on Friday, Dr. Anthony Fauci said the "full brunt" of Thanksgiving coronavirus cases won't be clear for another week or two.
"We'll see more of the surge as we get two to three weeks past (and) it butts right up on the Christmas holiday, as people start to travel and shop and congregate," Fauci said.
Fauci, director of the National Institute of Allergy and Infectious Diseases, said he accepted President-elect Joe Biden's offer to serve as his chief medical adviser "right on the spot."
Fauci said he supports as a "good idea" Biden's plan to suggest all Americans wear a mask for the first 100 days of his presidency.
Dr. Celine Gounder, a member of the Biden-Harris transition COVID-19 advisory board, said the incoming administration doesn't plan a national shutdown.
"Shutdowns, or lockdowns, are really not on the table, at least not from the Biden-Harris team. We really view this as restrictions that you dial up or dial down based on the local epidemiology," Gounder said.
California hospitals are treating about 2,066 COVID-19 patients in intensive care units, according to data from the state's Health Department. That's the highest number since the pandemic's start.
The figure comes as Gov. Gavin Newsom announced a strict regional stay-at-home order. The order will go into effect 48 hours after ICU capacity drops below 15% in one of five regions: Northern California, Bay Area, Greater Sacramento, San Joaquin Valley and Southern California.
Delaware Gov. John Carney announced Thursday a stay-at-home advisory, telling residents to avoid indoor gatherings with anyone outside their households from December 14 through January 11. The state also will require residents to wear cloth face coverings every time they're indoors with someone who isn't in their households, the governor's office said.
"A vaccine is on the way but, make no mistake, we are facing the most difficult few months of this crisis," the governor said in a statement. "I know we're all tired of COVID-19 -- but it's not tired of us."
Governors expect first vaccine doses to arrive soon
Meanwhile, local and state leaders have begun giving updates on when they expect their first batches of vaccines. No vaccine has received emergency use authorization from the Food and Drug Administration.
New York City Mayor Bill de Blasio said Thursday he expects the first round in about 12 days from Pfizer. About a week later, the city will get vaccines from Moderna.
The priority for distribution will be high-risk health care workers and residents, and workers in nursing homes, he said.
"Over time, there will be enough vaccines for everyone," de Blasio said.
Massachusetts Gov. Charlie Baker said he expects about 300,000 doses of a COVID-19 vaccine by the end of the month. Health care workers and long-term care facility residents and staff are "absolutely going to be up near the top of the list" for the first doses, Baker said.
This meshes with the COVID-19 vaccine recommendations voted on this week by the CDC's Advisory Committee on Immunization Practices and accepted by Redfield, head of the CDC.
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