Estes Hills Elementary School

Health officials are warning parents to be on alert. They said the seven infected students at the school were either related or had close contact with each other. Teachers sent home letters everyone who has had close contact with the children, and all of the school nurses are on alert looking for symptoms of coughing.

A vaccination for whooping cough, or pertussis, is required by the state for all children before going into kindergarten.

"Any vaccine is not 100 percent effective, so even though you've had the vaccine you still may be at risk,” Orange County Health Department Director Rosmary Summers said.

She said the highest risk groups are infants and the elderly.

"Those are the ones, who, if they got pertussis, would have a serious illness, perhaps would be hospitalized," Summers said.

Health officials said family or friends who come into close contact with those affected are usually the only ones at risk, but parents should still keep a close watch out for symptoms.

"It's a particular cough that you don't have a pause in between. You just have to keep coughing, so you can barely catch your breath,” said Summers. “At the end of the cough, there's sort of the classic 'whoop' or inhalation that gives you that strange sound."

Summers warned that with the holidays ahead, it's important to remember family members who may be at high risk.