Whooping cough — also known as pertussis — is rising sharply in Washington state, with 319 cases so far this year compared with 49 during the same period in 2014.

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Whooping cough is on the rise again in Washington state, with more than five times as many cases so far this year as in 2014. Vaccination of pregnant women, children and teens is the most effective way to stop the spread, health officials said.

As of April, there have been 319 cases of whooping cough, formally known as pertussis, compared with 49 cases for the same period last year, the state Department of Health reported.

That’s high, but not on track to reach the epidemic level of 2012, when nearly 5,000 cases were reported in the state. Still, Dr. Scott Lindquist, the state epidemiologist for communicable disease, sent warning letters about potential pertussis outbreaks to health providers this week.

“I’m calling it early because I want everyone to be aware,” he said, noting spikes of the disease in Kitsap and Walla Walla counties that may be spreading elsewhere.

Pertussis is a cyclical disease that peaks every three to five years. In recent years, the state and the nation have seen increased activity during the high points of such cycles, possibly because of changes in the type of vaccine used to prevent the disease, said Dr. Jeff Duchin, interim health officer for Public Health — Seattle & King County.

Because of concerns about potential adverse reactions to so-called whole-cell pertussis vaccines, manufacturers began making and using acellular vaccines. They are less likely to provoke reactions because they contain purified components of the Bordetella pertussis bacterium — but they also may not protect as long as the whole-cell version, experts say.

Throughout the 1990s, the U.S. switched from whole-cell vaccines to using the acellular vaccines in children. The first cohort of kids vaccinated completely with those acellular vaccines experienced waning immunity, which may have contributed to the 2012 epidemic, Duchin said.

“We are likely entering a long-term phase of cyclical activity at higher levels than we saw when more young persons had one or more doses of whole-cell vaccine,” he said.

Some experts believe the pertussis organism is mutating away from the strain covered by the vaccine, which also could contribute to the rising number of cases.

The single most important intervention is for pregnant women to be vaccinated, which not only protects the mothers, but also produces antibodies in their newborns, Lindquist said.

Infections in older children are driving the current cases, so parents should make sure teens have received booster doses. If they fall ill, seek medical attention, including testing for pertussis and antibiotics to treat the disease, Lindquist advised.

The DTaP vaccine — diphtheria, tetanus, pertussis — is approved for children younger than 7. The Tdap vaccine — tetanus, diphtheria, pertussis — is approved for older kids starting at age 11 and adults ages 19 and older. It is basically a booster dose that bumps up waning immunity.

Pertussis is a disease characterized by severe coughing that can cause serious and sometimes life-threatening complications in babies and young children, according to the Centers for Disease Control and Prevention. In 2014, 28,660 cases and nine deaths were reported in the U.S.