POULSBO — Kitsap County has not been immune to the whooping cough epidemic spreading through the state. Seventy-four percent of confirmed cases in the county are people that were vaccinated against whooping cough.

Health experts around the state are unclear why whooping cough has been spreading so rapidly since December, but an overall weakened immunity to the vaccine may be a factor, said Suzanne Plemmons, director of community health with Kitsap Public Health.

“We really don’t know for sure, the suspicion is over time, immunity wanes,” she said.

Plemmons said although health departments are looking into the effectiveness of the vaccine, known as Tdap, it is still important to continue to get vaccinated.

“It’s worth it to get it because people die, young infants [can] die from pertussis,” she said. “Even though it may not fully protect you, those people in the 74 percent, their disease was not as difficult as if they had not been vaccinated.”

As of May 23, there were 50 cases in Kitsap County since December — compared to 11 total cases in 2011 — but only six of those occurred in the north end of the county. Bainbridge Island and West Bremerton have the most reported cases compared to other Kitsap zip codes.

Robyn Chastain, director of communications for the North Kitsap School District, said they had not recieved any reports of whooping cough. Plemmons said a group of infectious disease experts, including Kitsap Public Health’s Director of Health Scott Lindquist, are working with the Department of Health and Centers for Disease Control.

Pertussis is known as whooping cough because of the “whooping” sound made by coughing. It is a highly contagious respiratory illness, spread by coughing and sneezing. Children are usually at least one year old before getting the pertussis vaccine, but pregnant women can get vaccinated to protect their infants.

The Department of Health recommends people substitute a Tdap vaccine for one routine tetanus booster, which is needed every 10 years, and people should get it sooner if they’re in close contact with young kids or live in an area where there are pertussis cases, according to a Washington State Department of Health release.

Health Secretary Mary Selecky declared the pertussis epidemic April 3. There have been more than 1,200 cases reported in 2012 throughout the state.

“The biggest thing is people should make sure they’re vaccinated,” Plemmons said. “People should stay home if they’re sick… cover your cough, wash your hands.”