A California school district is shutting down for two days due to "an immense strain" on the school system from rising COVID-19 cases.

The closures come despite a Dec. 22 statement from Gov. Gavin Newsom affirming state leaders' "shared commitment … to keep each other safe and to keep our classrooms open."

"Across California, school communities – students, parents, teachers, staff, administrators and board members together – have worked tirelessly to keep schools both safe and in-person. California schools have been open because of, not despite of, our priority on safety," Newsom said at the time. "As we approach the new year, we reaffirm our shared commitment to one another, to our parents and to our students: to keep each other safe and to keep our classrooms open."

Joy Harrison instructs her second graders at Carl B. Munck Elementary School, in Oakland, California. (Santiago Mejia/San Francisco Chronicle via AP, Pool, File)

Joy Harrison instructs her second graders at Carl B. Munck Elementary School, in Oakland, California. (Santiago Mejia/San Francisco Chronicle via AP, Pool, File)

But COVID-19 cases are spiking again across the country as the omicron variant continues its rapid spread, making up the vast majority of confirmed U.S. cases.

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West Contra Costa Unified School District (WCCUSD) Superintendent Kenneth Chris Hurst said in a notice this week that the omicron variant "is greatly impacting" schools.

"In our district, we are seeing far more staff absences than usual because of the virus, and we also have an increased number of students testing positive for COVID-19 as we return from winter break," he said. "This is putting an immense strain on our system. The rapid spread of the virus requires an aggressive response to ensure safety."

Hurst then announced class cancellations on Friday, Jan. 7, and Monday, Jan. 10, to "alleviate some of the pressure" on schools "and allow more time for those" in the community "who are out sick to heal."

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"The safety of our students and staff is our top priority, and closing school to prevent further outbreaks is an action we take very seriously and will only do when it is absolutely necessary. I do encourage all of our students and staff to quarantine as much as possible during the [days off]," he continued.

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Contra Costa County has recorded a seven-day average of 1,263.6 cases and 0.4 deaths as of Thursday, according to the Los Angeles Times' COVID-19 tracker. More than 85% of county residents have been at least partially vaccinated.

A spokesperson from Newsom's office told FoxNews.com in a statement that "in-person instruction is best for our students and, with California’s strong public health measures, can be done safely."

"Some school districts are taking temporary measures to manage short-term staffing shortages, such as utilizing off-days already built into their calendars (e.g., snow or air quality days)," the spokesperson said. "Schools are the safest places in our communities and our children greatly benefit from in person learning.  Throughout this last school year, California has proven that we can keep our students and teachers safe, with nation-leading safety measures such as vaccinations and masking. It’s why California accounts for 12% of the nation’s students and only 0.3% of school closures. The current spike in case rates should be a clarion call to continue those policies and encourage those who remain hesitant to get vaccinated and boosted as we endure this spike in cases throughout the country."

A student waits to receive the COVID-19 vaccine at the Woodrow Wilson Senior High School in Los Angeles, California, on Aug. 30, 2021.

A student waits to receive the COVID-19 vaccine at the Woodrow Wilson Senior High School in Los Angeles, California, on Aug. 30, 2021. (Getty Images)

Contra Costa currently has 119 hospitalizations, according to the county's website.

Residents between the ages of 19 and 50 make up the most cases while children 18 and under make up the second-most.

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Most public schools in California were closed for more than a year between March 2020 and the spring 2021.

COVID-19 case surges and severe winter weather have closed nearly 5,000 U.S. schools this week, according to independent community events tracking website Burbio, which has been tracking school closures over the course of the pandemic.