Prioritizing teachers in the distribution of Covid vaccines will continue to be a challenge until more doses become available, Andy Slavitt, senior advisor to the White House’s Covid-19 Response Team, said Wednesday.

President Joe Biden has made reopening the country’s schools for personal teaching a top priority.

On Friday, the Centers for Disease Control and Prevention published new guidelines that teachers shouldn’t be vaccinated to safely reopen schools, but that states should give teachers priority access to Covid vaccines.

Slavitt said governors had “tough decisions” to make to juggle vaccine distribution to groups like seniors, nursing home workers and teachers.

“We are trying to support them with science as much as possible, but until the shortage is fixed we will still have these challenges,” Slavitt told CNBC’s “The News with Shepard Smith”.

The question of whether teachers should be vaccinated before returning to class has been a focal point in the debate about reopening in-person teaching.

Vice President Kamala Harris said on the Today Show Wednesday morning, “Teachers should be priority.”

During a briefing on Wednesday, White House senior Covid-19 coordinator Jeff Zients said that while Biden and Harris believe that frontline teachers and other frontline staff should be on the front lines to get vaccines, they both do The CDC agree that vaccination of teachers “is not a requirement for schools to reopen.”

The CDC guidelines also recommend that schools adapt their reopening plans to the severity of the outbreak in their communities. The agency also recommends schools maintain “essential elements” of personal learning, including wearing masks, exercising physical distancing and monitoring the spread in the area.

“If that were easy, it would be done,” Slavitt told CNBC. “We’re focusing on how we get kids and teachers back to school – not if we should, but how. And that’s the CDC plan, in my opinion.”