School districts nationwide are facing a worsening teacher shortage because of the coronavirus, further complicating the tough decisions about whether to have in-person classes.

Why it matters: When teachers test positive, fall seriously ill or are self-isolating from potential exposure, many districts don't have enough substitutes to keep up.

Where it stands: There's early evidence children and schools are not major vectors of the virus, especially with proper social distancing, ventilation and mask requirements, but the risk for adults at school is not zero.

• Districts in Tennessee, Michigan and Maine and many other parts of the country have dozens of teachers absent at a time and had to close classrooms.
• Since the beginning of the 2020-21 school year, at least 751 Arizona teachers have resigned or quit, according to the Arizona Schools Personnel Administrators Association.
• The risk of infection has also triggered some early retirements and sick-outs.

What they're saying: Teachers have demanded more personal protective equipment and better ventilation to help manage the risk.

• But the absence of safety measures or unified guidance has put "teachers in a terrible, terrible position where the the only thing they can advocate for is having remote education," said Randi Weingarten, the president of the American Federation of Teachers.
• "At the end of the day you needed double the space and double the number of teachers in order to deal with this pandemic," Weingarten said.

By the numbers: 1.5 million teachers in the U.S. have health conditions that put them at higher risk of serious illness from COVID-19, per a Kaiser Family Foundation analysis.

• AFT and the National Education Association have estimated roughly 54 to 68 deaths among teachers, though data is limited.

The bottom line: "The consequences of doing the job poorly or doing it when it’s not feasibly safe are very very serious," said Noelle Ellerson Ng, associate executive director at the AASA, the School Superintendents Association.