UNITED NATIONS, Jan. 12 (Xinhua) -- Schools should be kept open or reopened as soon as possible, despite the COVID-19 pandemic, the United Nations Children's Fund (UNICEF) chief said on Tuesday.

"As we enter the second year of the COVID-19 pandemic, and as cases continue to soar around the world, no effort should be spared to keep schools open or prioritize them in reopening plans," said UNICEF Executive Director Henrietta Fore in a statement released on Tuesday.

Many countries have opted to keep schools closed, some for nearly a year.

She said there is overwhelming evidence of the impact that school closures have on children and increasing evidence that schools are not drivers of the pandemic.

"The cost of closing schools -- which at the peak of pandemic lockdowns affected 90 percent of students worldwide and left more than a third of schoolchildren with no access to remote education -- has been devastating," Fore said.

"The number of out-of-school children is about to increase by 24 million, to a level we have not seen in years and have fought so hard to overcome," the executive director said.

"Children's ability to read, write and do basic math has suffered, and the skills they need to thrive in the 21st century economy have diminished," Fore said. "Their health, development, safety and well-being are at risk. The most vulnerable among them will bear the heaviest brunt."

The executive director said that the closing of schools must be a measure of last resort, "after all other options have been considered."