By Dan Frosch, Elizabeth Findell and Peter Loftus

The U.S. is about to launch one of the most daunting public-health efforts in generations: swiftly distributing a Covid-19 vaccine across all 50 states, each of which will determine who gets priority.

As soon as this weekend, the Food and Drug Administration is expected to grant emergency approval to a Covid-19 vaccine from Pfizer Inc. and BioNTech SE. Within 24 hours, 6.4 million doses are set to be sent to every state and the District of Columbia. For most, that initial shipment will be enough to inoculate a little under 1% of their populations.

Most states are giving the initial batch to doctors, nurses and other health-care workers who interact with infected patients. As more doses are shipped, many said they would give priority to residents of long-term-care facilities next. The bulk of the population is expected to get the vaccine in the spring or summer, officials have said.

But state vaccination plans vary widely and leave many questions unanswered. Health officials are having to prioritize among competing groups including older adults, teachers and minority communities disproportionately affected by Covid-19. Many states also face challenges getting the vaccine to dramatically different populations, from crowded and diverse cities to isolated rural towns.

And they have to do it while coping with a surge in coronavirus cases already straining resources in many parts of the nation.

"This is going to be one of the biggest public health endeavors we've undertaken as a country," said Amesh A. Adalja, senior scholar at the Johns Hopkins Center for Health Security. "It's not just a done deal once we have a vaccine. It is going to be a process that's going to have hiccups and issues with supply chains and issues that are unanticipated."

About a week after the initial Pfizer shipment, about 12.5 million doses of Moderna Inc.'s vaccine are expected to be sent out if it also receives FDA authorization. Both vaccines are given in two doses, three or four weeks apart. Federal officials say they expect to distribute enough vaccines in December to immunize about 20 million people.

Supplies are expected to increase in January and beyond. Federal officials say they expect to have enough Covid-19 vaccine doses to immunize about 100 million people in the U.S. by the end of February. More will come in the spring and summer as people who weren't among the first groups to get doses begin to get vaccinated.

Along with vaccine vials, distribution sites will receive record cards for recipients noting which vaccine they received and when they are due back for the second shot.

While the federal government is issuing recommendations on whom to vaccinate first and how to allocate the doses, the final decisions and logistics are left up to states. Most of the states' plans remain in draft form. Some have hundreds of pages of details, while others are a few dozen pages long.

Ohio and Wisconsin are creating algorithms that will give priority to shipments based on criteria including county population and current infection rates. Hawaii, whose plan is 230-pages long, includes maps of where the most vulnerable populations are by island relative to the closest medical facilities.

Texas, whose draft plan is 38 pages, leaves many logistics up to local authorities.

"States are in very different places of being ready for this," said Jennifer Kates, a senior vice president for the nonprofit Kaiser Family Foundation, which analyzed the state plans. "They are in varying places of being able to even identify the universe of people that they're going to be reaching at different phases."

In Texas, the Pfizer vaccine, which ships in large quantities and requires storage at minus 94 degrees Fahrenheit, will initially be sent directly to hospitals large enough to immunize at least 1,000 workers immediately, state officials said. Meanwhile, rural communities will have to wait for the Moderna vaccine, which can be stored in a standard freezer, highlighting a challenge that many sparsely populated parts of the country will face.

In Ohio, state officials are planning to break down the large Pfizer shipments into smaller batches so they can be more flexible with distribution. Local health staff have been running drills in a central warehouse to ensure they can divvy up the vaccines safely, according to the Ohio Hospital Association.

Tensions over the order of the line for vaccines are likely to emerge as more shipments roll out, public-health experts say.

Several states in their draft plans give precedent to first responders such as police and firefighters over long-term-care residents, but that may change after the Centers for Disease Control and Prevention last week recommended moving up nursing home residents. The American Health Care Association, which represents long-term-care facilities, is pushing states to put their workers and residents first.

"A one-month delay in administering the vaccine at long-term-care facilities could cost more than 10,000 of our residents their lives," the association said.

In Florida, Gov. Ron DeSantis said residents of long-term-care facilities for the elderly are his priority, though his state's draft plan says front-line health workers come first. Spokespeople for Florida's health department didn't respond to a request for comment.

Arizona Gov. Doug Ducey said teachers would be among those to get the vaccine immediately in his state.

Education associations sent a letter to the CDC last month arguing that school personnel should be a priority group for immunizations, to allow in-person classes.

Black Americans, Latinos and Native Americans have all been disproportionately affected by Covid-19, studies show. According to the Kaiser Foundation, a majority of the state plans specifically mentioned focusing on minority groups or underserved populations for vaccination. Plans in states including North Carolina say minority groups may harbor skepticism about vaccines due to past inequities in medical treatment and call for crafting messaging aimed to build trust.

This month's vaccine shipments won't be enough to vaccinate all health workers and long-term-care residents -- estimated by the CDC to total 24 million people combined -- forcing state officials to further prioritize within those groups until more supply comes.

California will receive an initial shipment of 327,000 doses of Pfizer's vaccine for its population of about 40 million people, officials said. The state is creating subsets of health-care workers to identify those at greatest risk, such as people who work in inpatient care versus outpatient.

Roberta Schwartz, executive vice president of the seven hospital Houston Methodist health system in Texas, is figuring out what to do with 13,000 doses. First, her system will immunize its own employees, then workers at smaller nearby facilities, Ms. Schwartz said. Anyone with a Houston Methodist email address can make an appointment to get vaccinated, though employees directly in contact with patients will go first.

"The information changes now every 12 to 24 hours," she said. "We describe this as building the plane and flying it at the same time."

The Department of Veterans Affairs health-care system and the Indian Health Service are both receiving initial shipments and disseminating them among thousands of health-care workers within their own agencies.

For communities with fewer health-care resources, distributing vaccines while also dealing with Covid-19 cases will be particularly difficult. Many states have seen intensive-care units near or at capacity and shortages of qualified health-care workers because some are sick or quarantining.

"This is happening at a time when our hospitals and health-care personnel are being pushed to the limit by higher cases and more hospitalizations, creating even more strain on a public health-care system in near crisis," said Matt Nerzig, a spokesman for New Mexico Gov. Michelle Lujan Grisham.

To address the issue, some hospitals may have emergency medical technicians or pharmacy staffers administer vaccines, said Mike Abrams, chief executive of the Ohio Hospital Association.

But state officials say that the prospect of vaccinations effectively ending the pandemic by late 2021 is a light at the end of the tunnel.

"It's not going to be a smooth ride; it's going to be bumpy," said Eddy Bresnitz, medical adviser to New Jersey's health commissioner, focusing on the Covid-19 response. "But that's OK. We'll get to the finish line."

--Jim Carlton, Ian Lovett and Betsy McKay contributed to this article.

Write to Dan Frosch at dan.frosch@wsj.com, Elizabeth Findell at Elizabeth.Findell@wsj.com and Peter Loftus at peter.loftus@wsj.com

(END) Dow Jones Newswires

12-09-20 1521ET