A case of whooping cough prompted a cautionary message to parents of students at one Orange County elementary school.

The letter from Orange County Health director Quintana Stewart was sent to parents of students at Grady Brown Elementary School in Hillsborough late last week. Stewart wrote that the department “has identified one confirmed case of Pertussis” at the school.

Orange County Health Department spokesperson Kristin Prelipp told WCHL that two cases of whooping cough were confirmed in a nine-year-old student at Grady Brown Elementary and their nine-month-old sibling.

Both children were vaccinated, according to Prelipp. The letter sent to parents said that the vaccinations are effective in “preventing disease in 80%-85% of those who are vaccinated.”

This letter comes after a whooping cough outbreak earlier this year. There were 20 cases of Pertussis during that outbreak, according to an email from Stewart to other officials.

An outbreak is defined as being three or more unrelated cases of whooping cough.

The Centers for Disease Control and Prevention says that whooping cough “usually starts with cold-like symptoms and maybe a mild cough or fever.”

As the disease progresses, symptoms evolve to fits of rapid coughs, vomiting and exhaustion.

While both children affected by whooping cough in this scenario were vaccinated, the CDC maintains the Pertussis vaccine is beneficial and important to prevention.