California is in the throes of a whooping cough epidemic, state health department officials announced Friday.

Dr. Ron Chapman, director of the California Department of Public Health, said 3,458 cases of whooping cough have been reported since Jan. 1 — including 800 in the past two weeks. That total is more than all the cases reported in 2013.

“Preventing severe disease and death in infants is our highest priority,” Chapman said in a statement. “We urge all pregnant women to get vaccinated. We also urge parents to vaccinate infants as soon as possible.”

Whooping cough, or pertussis, is cyclical and peaks every three to five years. The last peak in California occurred in 2010, when a total of 9,159 cases were reported. Chapman said it is likely another peak is underway.

Health department officials say infants too young to be fully immunized remain most vulnerable to severe and fatal cases of pertussis. Two-thirds of pertussis hospitalizations have been in children four months or younger. Two infant deaths have been reported.

The Tdap vaccination for pregnant women is the best way to protect infants who are too young to be vaccinated, health officials say.

All pregnant women should be vaccinated with Tdap in the third trimester of each pregnancy, regardless of previous Tdap vaccination. In addition, infants should be vaccinated as soon as possible. The first dose of pertussis vaccine can be given as early as 6 weeks of age.

Older children, pre-adolescents, and adults also should also be vaccinated against pertussis according to current recommendations. It is particularly important that persons who will be around newborns also be vaccinated.

“Unlike some other vaccine-preventable diseases, like measles, neither vaccination nor illness from pertussis offers lifetime immunity,” said Chapman. “However, vaccination is still the best defense against this potentially fatal disease.”

Symptoms of pertussis vary by age. For children, a typical case of pertussis starts with a cough and runny nose for one to two weeks. The cough then worsens and children may have rapid coughing spells that end with a “whooping” sound.

Young infants may not have typical pertussis symptoms and may have no apparent cough. Parents may describe episodes in which the infant’s face turns red or purple. For adults, pertussis may simply be a cough that persists for several weeks.

Contact Tracy Seipel at 408-920-5343. Follow her at Twitter.com/taseipel.