BETHESDA, MD 19 July 2012—More than 3,000 pertussis cases have been reported in Washington state this year, a national high in what is on track to be a big year for the disease.

"There is a lot of pertussis out there, and I think there may be more coming to a place near you," said Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention (CDC).

Schuchat told reporters today that nearly 18,000 pertussis cases have been reported to CDC so far this year, more than twice the number reported at the same time last year. Nine children have died from pertussis this year, she said.

Shhuchat said the nation has not had an epidemic of pertussis of this magnitude since the late 1950s, and she urged everyone whose vaccination status is not current to get vaccinated against the disease.

Pregnant women, health care workers, and other adults who have close contact with infants are the most critical groups to get vaccinated because of the exposure risk they pose to infants too young to receive pertussis vaccine, Schuchat said.

Washington. Mary Selecky, secretary of the Washington State Department of Health, declared a pertussis epidemic in the state on April 3. She said today that the number of confirmed cases in Washington is three times higher than during all of last year.

But she said the numbers probably underestimate the true burden of disease.

"For every case we know about, we expect there are many people out there who have pertussis and don't know about it," Selecky said.

The Washington state pertussis epidemic is described in CDC's July 20 Morbidity and Mortality Weekly Report (PDF).

No pertussis-related deaths have been reported so far in the state, although two children under age 1 year died of the disease during the each of the past two years, Selecky said.

In response to the epidemic, the state health department has already distributed throughout Washington 27,000 doses of Tdap vaccine and has ordered more, Selecky said.

The Tdap vaccine protects against tetanus, diphtheria, and pertussis and has been licensed in the United States since 1997. The pertussis component of this vaccine is acellular, in contrast to earlier versions, which contained whole-cell pertussis antigens.

New disease patterns.. According to CDC, data from Washington state and around the country indicate that pertussis rates are unusually high among 13–14-year-olds and may reflect a waning of the protective effect of the acellular vaccine component when it is administered as a booster in children ages 11–12 years.

Pertussis infection rates have been rising nationally for several years in children ages 7–11 years as well, which indicates that acellular pertussis vaccines administered earlier in infancy and childhood did not provide long-term protection, CDC stated.

Infection rate are lower in adolescents and young adults age 15–19 years of age whose pertussis-vaccine regimen would have consisted all or in part of whole-cell vaccines.

CDC stated that it is evaluating the effectiveness and duration of immunity in children and adolescents in Washington and California who received acellular pertussis-containing vaccines.