SAN DIEGO -- Two children at a San Diego charter school and a sibling have contracted measles, prompting county health officials Monday to notify parents and students about possible exposure.

Two of the children attended the San Diego Cooperative Charter School, according to the San Diego County Health and Human Services Agency.

They did not have the measles vaccine, according to the HHSA.

"This underscores the importance of vaccinating children for measles and other vaccine-preventable diseases," said Dr. Wilma Wooten, San Diego County's public health officer.

Health officials said children should get the measles, mumps and rubella, or MMR, vaccine at 12 months, and again between 4 and 6 years old.

This is the first local "cluster" of measles in children in the San Diego area since 1991, according to the HHSA. There have been four isolated cases of measles in the county since 2003.

School officials have called parents and sent letters and e-mails warning them about possible exposure, according to HHSA.

"We are working with HHSA to educate parents about measles and are providing resources if they have further questions," said Wendy Ranck-Buhr, principal of Cooperative Charter School.

Measles is a highly contagious viral disease, according to the HHSA. It is easily spread by coughing, sneezing or close contact with an infected person.

The disease causes a rash, high fever, cough, runny nose and watery eyes, usually lasting for one to two weeks, according to the HHSA. It can be spread from four days before the rash appears to four days after.

Health officials said the rash begins on the face and head then proceeds down and out to the hands and feet.

Complications from measles are more common in children younger than five, and adults 20 or older, according to the HHSA. Death can occur from severe complications and the risk is higher among younger children and adults, county health officials said.