(CNN) The US set a record Tuesday for the most Covid-19 deaths reported in one day since the start of the pandemic, according to data from Johns Hopkins University.
As of Tuesday evening, 4,197 deaths were reported, according to JHU. This is not the complete total for Tuesday, though, because final numbers come in overnight.
The only other time the number of deaths have gone over 4,000 took place on January 7 when 4,194 total deaths were reported, according to JHU data.
Prior to Tuesday's record-setting death toll, the US had averaged more than 3,223 Covid-19 deaths a day over the past week, JHU data showed.
After widespread concerns about delays in vaccinations, the Trump administration will now release reserved second doses immediately, US Health and Human Services Secretary Alex Azar said.
Such a plan had already been announced by President-elect Joe Biden.
More than 9 million people have received their first dose of the coronavirus vaccine and more than 27 million doses have been distributed, according to the US Centers for Disease Control and Prevention. That means one-third of vaccines that have been delivered have been given to people.
Six states -- North Dakota, West Virginia, Connecticut, South Dakota, Montana and Tennessee -- have administered enough first doses to account for more than half of the doses they've received.
Meanwhile, seven states -- Arkansas, Georgia, Alabama, Hawaii, Virginia, Idaho and California -- have administered less than a quarter of the doses they've received.
Officials with Operation Warp Speed defended the slow rollout of vaccines Tuesday, saying states were sticking too rigidly to guidance designating health care workers and nursing home residents to be vaccinated first. They said the rollout would speed up soon, and asked states to open up vaccination to everyone 65 and older and to younger people with chronic conditions.
Over the past week, an average of 248,650 new Covid-19 infections have been reported every day.
The massive surge of Covid-19 nationwide has been fueled by holiday travels and casual at-home gatherings that experts had warned against.
"This is what we were afraid of -- people letting their guard down over Christmas and New Year's," New Jersey Gov. Phil Murphy said.
The federal government has been holding back about half the available doses from vaccine makers Moderna and Pfizer to make sure everyone who gets a first dose gets their second needed dose on time.
The Pfizer vaccine doses should be spaced 21 days apart, and the Moderna doses should be 28 days apart.
But on Tuesday, Azar said, "We do not need to hold back reserve doses" anymore.
"Every vaccine dose that is sitting in a warehouse without going into an arm could mean one more life lost or another hospital bed occupied," Azar said.
If any glitches happen with vaccine production, any new doses would be designated as second doses.
In addition to releasing reserved doses immediately, HHS announced vaccines will be distributed to states based on which jurisdictions are getting the most doses into arms and where the most older adults live.
That new strategy will begin in two weeks, Azar said Tuesday.
"We will be allocating them based on the pace of administration as reported by states and by the size of the 65 and over population in each state. We're giving states two weeks' notice of this shift to give them the time necessary to plan and to improve their reporting if they think their data is faulty," Azar said.
"This new system gives states a strong incentive to ensure that all vaccinations are being properly reported, which it currently is not, and it gives states a strong incentive to ensure doses are going to work," he said.
"We need doses going to where they'll be administered quickly and to where they'll protect the most vulnerable."
About 9 million people have now received the first dose of a Covid-19 vaccine, and more than 25.4 million doses have been distributed across the US, according to data from the US Centers for Disease Control and Prevention.
Amid a rollout that has been far slower than some officials hoped, more states are abandoning guidelines from the CDC and taking their own approach to administering the vaccine, a new analysis found.
Timelines vary across the country and "access to Covid-19 vaccines in these first months of the US vaccine campaign may depend a great deal on where one lives," the Kaiser Family Foundation, which studies health care policy, said in a report issued Monday.
The report found 40 states are still in Phase 1a -- when the CDC recommends vaccinating health care workers and long-term care facility residents -- either fully or partly. Ten states and Washington DC were in Phase 1b. Only Michigan has moved to at least part of Phase 1c, the report said.
For Phase 1b, CDC recommends vaccinating people age 75 and older and frontline essential workers and for Phase 1c, the agency recommends the vaccinations of people 65 and older, younger people with high-risk conditions and other essential workers.
States are "making the decision to just get as many people vaccinated as they can," and bypassing recommendations for vaccine prioritization, said Dr. Paul Offit, a member of the FDA's vaccine advisory committee on Monday.
"I think where people are right now is they have the vaccine and they just want to get it out there," Offit said.
Without the "public health infrastructure for mass vaccination" in place, states are having to learn how to manage mass vaccinations in real time, and some are learning quicker than others, he added.
In at least 10 states, National Guard members are helping administer vaccines. Other states have asked dentists, retirees and students to aid in the process.
In Texas, Gov. Greg Abbott toured a mass Covid-19 vaccination site Monday and said the state plans to open about 28 similar sites across 18 counties.
"These vaccination hubs will expedite vaccine distribution and ensure efficiency in communities across the state," the governor said.
In California, 1 million health care workers, nursing home residents and staff will receive the vaccine by week's end, the governor promised Monday, as part of an "all hands on deck" push to serve the more vulnerable residents.
Michigan Gov. Gretchen Whitmer, meanwhile, sent a letter to Azar requesting permission to buy up to 100,000 doses of vaccines for the state.
"We remain ready to accelerate distribution to get doses into arms," the governor said.
The letter comes after Whitmer and other state leaders urged government officials to distribute the vaccine doses that are currently being held back by the Trump administration.
The CDC announced Tuesday an order requiring all airline passengers entering the United States to show proof of a negative Covid-19 test before boarding flights to the US.
"Testing does not eliminate all risk," CDC Director Robert Redfield said in a statement. "But when combined with a period of staying at home and everyday precautions like wearing masks and social distancing, it can make travel safer, healthier, and more responsible by reducing spread on planes, in airports, and at destinations."
This order will go into effect on January 26, the CDC said.
The rule is similar to one put in place last month for passengers from the United Kingdom to the US, which requires that passengers have a negative test within three days of boarding their flight.
For the UK requirement that went through last month, airlines can be subject to criminal penalties if they fail to comply, and passengers can be subject to criminal penalties if they willfully give false or misleading information.