It's back to school time in America after a year of remote learning, but forget about the iconic yellow school bus: because of Covid, there is a shortage of drivers.

The problem -- among other issues -- is that some drivers oppose mask-wearing mandates, and others, who are older and do this kind work after retiring from other jobs, are worried about catching the virus while driving kids around, education officials said.

The Minneapolis area of Minnesota, for instance, has warned that school bus service this year will be sporadic because of what it called a driver shortage being faced by school districts around the country.

"Minneapolis Public Schools is encouraging families who can transport their students to school on their own to do so," the local school district said.

And one private school in Wilmington, Delaware, the home town of President Joe Biden, is offering parents $700 a year to drive their kids to school.

Back to school day is not uniform across the country; some kids resumed class in late July and others will not do so until September.

Because of the transportation problem some districts, like the schools in Pittsburgh, have given kids two weeks of extra vacation while they try to sort out the bus issue. There, officials still need to find bus seats for 5,000 children.

Mask mandate scares some away

School bus drivers have been in short supply for some time in the United States, but the pandemic has made things worse.

Greg Jackson, director of transportation for Jeffco school district in Colorado, said his area has a lot of retirement-age drivers who are particularly vulnerable to the virus and thus worried about returning to work.

Others oppose the district's policy of having drivers wear masks, he said, "so they didn't come back."

"We lost a few folks just recently because of that," Jackson said.

Across the country school officials are bending over backwards to get kids back to school with their classmates and teachers after all these months of trying to study and learn at home.

School office workers are being recruited to drive buses, for instance, bus routes are being extended to get more kids aboard and bus stops are being reorganized.

Waiting lists for bus service are now sometimes very long.

To lure people to work as bus drivers, salaries are being raised and signing bonuses of up to $4,000 are being offered.

'This is not a hoax'

Since the start of the pandemic the bus driver workforce has dwindled by one-quarter, the Bureau of Labor Statistics says.

Job recruiting sites now feature some 5,000 positions for school bus drivers, which is nearly double the pre-pandemic figure, Julia Pollak, an economist with ziprecruiter.com, told AFP.

"The average school bus driver's salary is about $34k per year, or $16 per hour. It is precisely in this pay bracket that employers are reporting the greatest difficulties filling vacancies, due to concerns about workplace health and safety, childcare barriers, and the financial cushion provided by Covid relief and stimulus spending," Pollak said.

Indeed, school bus drivers are not the only people in demand, as many US employers say they are having trouble hiring people in lower paying positions.

Even after people are hired as school bus drivers, it is not a done deal, said Jackson.

After the new recruits are trained to drive a bus, there is the risk they will take their brand new certification to the higher-paying private sector, he said.

"It happened a lot," he said.

"I hope that parents understand that this is not a hoax, because it's a national driver shortage," he said.

"The teams are doing everything they can every day to make sure that we can provide the best service we can. It's not going to be the same service we did before."