The US Covid-19 vaccination campaign has begun, and the few available doses are mostly going into the arms of healthcare workers and nursing home residents.

But what about in January, February and March, when more shots are expected to become available? Who should get those doses? A federal panel of vaccination experts takes up that question at an emergency meeting this weekend. No matter what the committee decides, there will be differences from state to state.

The panelists are leaning toward putting essential workers first because bus drivers, grocery store clerks and similar employees can’t work from home. They are the people getting infected most often, and where concerns about racial inequities in risk are most apparent.

But other experts say people age 65 and older should be next, along with people with certain medical conditions. Those are the people who are dying at the highest rates, they say.

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The group is scheduled to vote on the proposal Sunday, one day after it discusses a vaccine made by Moderna.

“I think we know this isn’t going to be perfect. We don’t have vaccine for everyone right away, so we’re going to have to make difficult decisions,” said Claire Hannan, executive director of an organisation that represents the managers of state vaccination programs.

If essential workers are indeed next up, states already have different ideas about who among them should be closer to the front of the line.

In Nevada, for example, teachers and child care staff will be ahead of public transport workers, according to the state’s current vaccination plan. Then come agriculture and food workers, and then retail and utility employees.

In South Dakota, teachers could get access before those working in food and transportation. In Arkansas, the essential workers list includes teachers, prison guards, cops, meatpacking plant workers and mayors.

The advice of the expert panel — the Advisory Committee on Immunisation Practices — is almost always endorsed by the US Centres for Disease Control and Prevention. That’s what happened earlier this month, when the group said top priority should be given to healthcare workers and residents of long-term care homes for the 20 million initial vaccination this month.

But it’s not clear things will go the same way in the next phase. The CDC’s director, Dr Robert Redfield, has said he believes priority should be given to people age 70 and older who live with children or grandchildren.

The advisory panel’s chairman, Dr Jose Romero, told The Associated Press he was aware of Redfield’s earlier comments but had not spoken directly with him about it.

Redfield declined to say if he would prioritise seniors over essential workers, even if the panel recommends the reverse. “I look forward to listening to the advisory group’s discussion, and to receiving its recommendation for consideration,” he said in an emailed statement to the AP.

Also read: Covid vaccine: UK frontline hospital staffs, senior citizens vaccinated

States don’t have to follow the guidance.

After the CDC panel said healthcare workers and nursing home residents should get the very first doses, most states followed those recommendations. But there have been a few exceptions. Utah said long-term care residents should be in line behind healthcare workers, instead of sharing the front with them. Massachusetts included prisoners and homeless people in the first tier while Nevada, New Hampshire and Wyoming did the same for police officers.

“State-to-state variations are likely increase in the next priority groups,” said the Kaiser Family Foundation’s Jennifer Kates, who has been analysing state vaccination plans.

“ I think we’re going to see states falling out in different ways, with some prioritising seniors over essential workers,” Kates said.

Things could get messy. For example, some experts said it’s possible that if one state prioritises certain essential workers and a neighbouring state decides to give primacy to seniors, people could try crossing state lines in hopes of getting vaccinated.

“That’s one of the issues of not having a fully national plan of immunisation,” said Romero, who also is the head of the Arkansas state health department.

The proposal before the advisory committee relies on a broad definition of essential workers set in August by the US Department of Homeland Security. It counts hundreds of different kinds of jobs as critical infrastructure workforce, including first responders, teachers, communications technicians, weather forecasters, sewage treatment plant employees and people who work in animal shelters.

According to estimates presented to the advisory committee, as many as 87 million people can be counted as essential employees who don’t work in healthcare.

The government expects to be able to start vaccinating only 80 million new people in the first three months of 2021.

It’s possible the committee might consider giving essential workers and seniors equal status, similar to how it said that both healthcare workers and nursing home residents should be together at the very front of the line. But that would create a priority group that is far, far larger than the number that can be vaccinated before spring.

The nation has more than 53 million seniors. The CDC also counts more than 100 million Americans as having underlying medical conditions that put them at higher risk for severe Covid-19-related illness, though there is overlap between the two groups.

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