A drastic increase in the number of whooping cough cases in California has health officials declaring it an epidemic.

Whooping cough, officially known as pertussis, is highly contagious. It is called whooping cough because of the “whooping sound” people are forced to make after a long coughing fit as explained by the Center for Disease Control and Prevention.

Just in the last two weeks alone, 800 cases of whooping cough have been reported in California. TheCalifornia Department of Public Health (CDPH) states that as of this June, they have had 3,458 cases of pertussis reported to them in 2014, exceeding the number seen in the entirety of 2013.

Infants and young children are especially susceptible and are the most commonly afflicted with the disease. According to the CDPH’s report, two-thirds of hospitalizations caused by whooping cough have been children four months old or younger.

Dr. Ron Chapman, director of the California Department of Public Health said in a public statement, “Preventing severe disease and death in infants is our highest priority. We urge all pregnant women to get vaccinated. We also urge parents to vaccinate infants as soon as possible.”

To protect their infants, pregnant women can be vaccinated against pertussis in their third trimester and infants can begin the vaccination process at 6 weeks old.