SAN DIEGO -- Eleven students at a Chula Vista elementary school have been diagnosed with chicken pox, the San Diego County Health and Human Services Agency announced Tuesday.

One third-grader, nine fifth-graders and one sixth-grader at Joseph Casillas Elementary School have been infected, according to the HHSA.

A dozen other students who are out of school with rashes may have also contracted chicken pox, but that has not been confirmed, according to the HHSA.

None of the students required hospitalization.

County health officials urged parents to get their children vaccinated against the disease.

"Diseases like chicken pox are preventable with vaccination, and we urge parents to ensure their children are inoculated against them," said Dr. Wilma Wooten, the county's public health officer. "Parents should check with their physicians to make sure their children have all the recommended vaccines."

Chicken pox is a highly contagious virus, easily spread by coughing, sneezing or contact with blisters. Symptoms include a skin rash of blister-like lesions, covering the body but are usually more concentrated on the face, scalp and trunk.