People over 75, front-line essential workers should get vaccine next, CDC panel says

Members of the National Guard will help distribute the COVID-19 vaccine in 26 U.S. states and territories, a National Guard official said during a press briefing Monday.

National Guard commanders from Ohio, West Virginia and Oklahoma detailed the limited role their members will play in their respective states.

It will work with state departments of health to break down the large 975-batch Pfizer packages into smaller packages as needed, and use rented vehicles and equipment to transfer packages from main hubs to satellite sites for further distribution.

ABC News' Matt Seyler contributed to this report

The number of confirmed deaths from COVID-19 in the United States surpassed 300,000 on Monday, according to real-time data from Johns Hopkins University.

The grim milestone comes after the U.S. logged 3,124 fatalities from the disease in a single day last week, the highest one-day COVID-19 death toll the country has reported since the pandemic began.

One of the biggest unanswered questions scientists have about the COVID-19 vaccine is how long virus protection will last after people get two doses.

While more research needs to be done before any official guidance is released, Dr. Peter Marks, director of the Center for Biologics Evaluation and Research at the U.S. Food and Drug Administration, said early vaccine trials may provide clues.

At the very least, a two-shot vaccination should offer at least several months of protection, Marks explained during an interview with the Journal of the American Medical Association on Monday.

"It's at least probably on the order of four to six months," Marks said. "The question is, will it reach out to a year? Hopefully, yes. But I think we’ll have those data in the not so different future."

ABC News' Anne Flaherty contributed to this report.

Twenty million Americans should be able to get the first dose of the COVID-19 vaccine by the end of December, and another 30 million by the end of January, Alex Azar, secretary of Health and Human Services, said during a Monday news briefing. By the end of March, 100 million people are projected to receive a first dose.

Gen. Gustave Perna, chief operating officer for Operation Warp Speed, said that long-term care facilities in four states would work in tandem with CVS and Walgreens to start vaccinating patients and staff this weekend. An estimated 1,100 long-term care and nursing home facilities will begin vaccination next Monday.

ABC News' Luis Martinez contributed to this report.