The number of school closures due to COVID-19 is increasing alongside pediatric infections as the country's public school system fully reopens – in many places with low vaccination rates and mask-optional policies.

More than 1,400 schools across 278 districts in 35 states that began the academic year in person have closed, according to Burbio, an organization that's tracking how schools respond to the ongoing pandemic. The figures are up from 698 schools across 158 districts in 25 states.

While the spike in the school closure count is startling many education officials whose well-laid back-to-school plans have been foisted by the highly contagious delta variant and is creating major challenges for parents, they make up just a fraction of the 98,000 public schools across the country.

In more than half of the closures, the schools pivoted to virtual instruction, but roughly 40% of schools that closed for a period of time did so without any remote learning plan in place, according to Burbio. A little less than 5% of schools delayed school start – some due to logistical issues like hiring enough bus drivers – and about 3% moved to a hybrid format, where students receive both in-person and virtual instruction.