Disease detectives hope to unravel the mystery of why Washington is in the midst of a whooping cough epidemic, with rates 10 times those reported last year.
For the past six weeks, dozens of federal disease detectives have been sleuthing in Washington state, combing through medical records, digging into the state’s immunization registry and quizzing doctors in a quest to unravel a mystery: Why is Washington in the midst of a whooping cough epidemic, with rates 10 times those reported last year?
According to data from the state and the Centers for Disease Control and Prevention (CDC), Washington has the third-highest rate of whooping cough cases in the nation.
Some 40 to 50 CDC “epidemic intelligence service” investigators are now heading back to the agency’s Atlanta headquarters, where epidemiologists will compile and analyze the data they’ve collected on Washington patients who contracted this disease, which is very contagious and can be deadly for infants.
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Kim Brinker, one of the few CDC sleuths still in the state, declined to speculate about that agency’s likely conclusions or possible action, which could include calling for a new vaccine formulation or recommending a different immunization schedule.
It was clear the investigators’ focus was on the vaccine’s staying quality — or lack thereof — when Brinker revealed they had looked only at the immunization records of patients ages 11 to 18, where the disease has hit particularly hard.
One big clue: The whopping majority — 77 percent — of 13- to 19-year-olds diagnosed with whooping cough in Washington had received their last recommended vaccination. Even more significant: This is the first generation of teenagers that has received only the new formulation of the vaccine.
That modern version of the vaccine, it appears, just isn’t lasting as long as expected.
Vaccines for whooping cough — “pertussis” in science-speak — switched in the late 1990s from a whole-cell vaccine (the DTP or DTwP) to a more highly purified “acellular” vaccine containing a smaller part of the bug.
The new acellular formulations cause fewer side effects such as fever or seizures, said Dr. Edgar Marcuse, a pediatrician, epidemiologist and vaccines expert at the University of Washington and Seattle Children’s.
Now, both the initial set of childhood pertussis vaccines, the DTaP series, and the Tdap vaccine, approved in 2005 for teens and adults to boost protection, are acellular vaccines (the “a” in the vaccines’ shorthand names).
As the cases pile up, they have allowed epidemiologists to see the big picture: The major spikes in cases are occurring in younger teens, up to about age 15, who have never gotten the whole-cell vaccine (the DTP or DTwP) and have received only the acellular vaccine, the DTaP and Tdap.
According to data published by the CDC this year, 16- to-19-year olds, who are old enough to have received the whole-cell vaccine in their first round of immunization as infants, have a much-reduced incidence of the disease.
The CDC is concerned the new vaccine isn’t creating an immune response that’s strong and long-lasting, Brinker said.
Although much has been made of some Washington residents’ reluctance to immunize their children, in fact, most parents are vaccinating their children against pertussis, acknowledged to be a bad bug. Of those children ages 3 months to 10 years who came down with pertussis, about 76 percent had received the recommended vaccines.
“We don’t think that (reluctance to vaccinate) is the driving force behind the rise in cases,” Brinker said, although non-vaccinated children are eight times more likely to come down with pertussis.
Pertussis, also called the “100-day cough,” is very contagious, and it’s particularly dangerous to infants, who can’t begin immunizations until about 2 months of age.
Caused by a bacterial infection, pertussis creates breathing difficulty, vomiting, and coughing so violent that patients have broken ribs; public-health officials take outbreaks very seriously. Brinker, a nurse-epidemiologist, said about 30,000 cases have been reported nationwide this year, with 14 deaths, primarily in infants, though none in Washington.
According to state and CDC data, Washington has more than 58 cases of pertussis per 100,000 people. Within the state, Skagit County has the highest rate, with 462 cases per 100,000.
The highest state rate is in Wisconsin, with nearly 79 cases per 100,000 people.
While there are outbreaks elsewhere around the world, including in Australia, Washington’s situation drew the CDC’s attention last spring, when the state declared an epidemic. The number of Washington cases so far this year is nearly 10 times that of last year: 4,190 cases versus 450. By June 20, the CDC notes, Washington already had reported more cases of whooping cough than in any year since 1942.
Why us and why now? Michele Roberts, immunization spokeswoman for the state’s Department of Health, Brinker and other public-health pertussis experts say the disease is cyclical, reaching high levels in a particular area one year and falling off in others.
The CDC isn’t singling out Washington, Roberts and Brinker said, but is sending investigators to places where high numbers of cases make data-gathering more efficient. They have visited California, which in 2010 experienced a large outbreak that prompted attention from researchers from the Kaiser Permanente Vaccine Study Center.
Their study, published in the New England Journal of Medicine this month, showed that protection against pertussis waned during the five years after the last dose of DTaP, typically given to children between ages 4 and 6.
Earlier studies, including one published in the same journal in 1996, which concluded the two formulations of the vaccine conferred equal protection, apparently did not follow its subjects long enough.
Although the researchers in the current study said the reasons for the outbreak “are not well understood,” they concluded there was a need to develop new pertussis-containing vaccines that will provide long-lasting immunity.
Brinker couldn’t speculate as to that possibility; the CDC’s vaccine recommendation process is complex and demanding. That’s why the investigators weren’t taking parents’ word for vaccination histories, instead searching out actual medical records and facts. That data is now destined for the CDC’s Advisory Committee on Immunization Practices, which will recommend the next steps.
Carol M. Ostrom: 206-464-2249 or firstname.lastname@example.org. On Twitter @costrom.