Officials have closed a Prince William County elementary school after it became the site of a coronavirus outbreak, forcing more than 700 students to learn online for at least a week.

The closure marks the first time the Northern Virginia county’s school system, which enrolls nearly 90,000, has shut down a campus this academic year. It is also one of the first such closures in the D.C. area, although the vast majority of the region’s children are back in classrooms this fall, some for the first time in 18 months.

The 735 students at Bennett Elementary School in Manassas began remote learning Tuesday and will continue attending classes online until at least Friday. Extracurricular activities are canceled for the duration of the closure, according to county schools spokeswoman Diana Gulotta.

The temporary reversion to virtual instruction is due to an outbreak that saw 36 coronavirus cases emerge at the school and sent more than 200 students into quarantine, Gulotta said. She said disease transmission apparently took place both inside and outside the school, although officials were unsure of the exact breakdown.

Gulotta said the district is working to return students to classrooms as swiftly as possible but declined to give a definitive date.

“We are hopeful about resuming in-person learning next Monday,” Oct. 18, Gulotta wrote in a statement Tuesday. “However, we will continue to monitor the data to ensure it is safe for students to return.”

The closure comes as the pace of the pandemic in the D.C. area appears to be slowing. The highly contagious delta variant is still driving infections, but the average number of new cases per week has declined recently in D.C., Maryland and Virginia.

Eric Toner, a senior scholar at the Johns Hopkins Center for Health Security, said it is unsurprising for a local school system to report such an outbreak even as infection rates drop in the region.

“Even as COVID-19 recedes, and even after the pandemic is officially over, there will still be isolated outbreaks,” Toner wrote in an email. “All that said, if this turns out to be the first of many school-based outbreaks, then that could undermine the progress we are currently seeing.”

He added that school systems must continue to follow mitigation strategies, such as mask-wearing.

Counties in the region with higher vaccination rates are experiencing fewer cases and hospitalizations, while areas with lower vaccination rates — including the Shenandoah Valley — are seeing record numbers of people hospitalized with the virus. About 70 percent of the population of D.C., Maryland and Virginia is vaccinated, according to a Washington Post data tracker.

In Prince William County, about 68 percent of residents 12 and older have received at least their first dose of a coronavirus vaccine, according to county health data. Nonetheless, Prince William is still experiencing a “high” level of transmission, according to the Virginia Health Department. In the week leading up to Oct. 3, the county reported that 151 people had tested positive for the virus, for a positivity rate of 5.3 percent.

In Prince William’s school system, 37 staff members and 183 students were isolating as of Tuesday because they tested positive for the virus. An additional nine staff members and 1,066 students are quarantining because of possible virus exposure.

In a message to families and employees Friday, Prince William Schools Superintendent LaTanya McDade wrote that no other school in the division is approaching a case load that would require closure.

“This step is being taken out of an abundance of caution to ensure the health and safety of all students and staff,” McDade wrote of the decision to shutter Bennett Elementary.

Spokespeople for the other four major Northern Virginia school systems — those in Alexandria, Arlington County, Loudoun County and Fairfax County — said they have not yet had to shutter a campus for a virus outbreak this year.