Why whooping cough has made a comeback
Weakened vaccines and heightened awareness of pertussis have contributed to its higher profile.
Thu, Aug 16, 2012 at 10:01 AM
The number of whooping cough cases in the U.S. this year is on track to be the highest in 50 years, although one researcher says the main reason behind the disease's apparent resurgence is a heightened awareness of it.
Besides improved reporting of cases of whooping cough (which is also called pertussis), factors in the disease's resurgence include the fact that vaccines don't completely protect against it, and that the current vaccine provides even less protection than previous ones did, according to Dr. James Cherry, a professor of pediatric infectious diseases at the David Geffen School of Medicine, University of California at Los Angeles.
"It is time to recognize the successes of the past, and to implement new studies and direction for the control of pertussis in the future," Cherry writes in an editorial published on Aug. 16 in the New England Journal of Medicine.
The whooping cough vaccine reduced the rate of the disease in the U.S. from 157 cases per 100,000 people in the early 1940s to fewer than one case per 100,000 in 1973, Cherry said. During the 1980s and most of the 1990s, the rate remained below three cases per 100,000. However, outbreaks over the past decade have brought spikes of nearly nine cases per 100,000.
"The timing of the initial resurgence of reported cases suggests that the main reason for it was actually increased awareness," Cherry said. In the 1970s and 1980s, the media brought attention to the question of vaccine safety, and in the 1980s and 1990s, studies of the vaccine in use today — called the "DTaP" vaccine, which protects against diphtheria, tetanus and pertussis — also raised awareness of the disease.
"Pediatricians, public health officials, and the public became more aware of pertussis, and reporting therefore improved," Cherry said.
Additionally, a technique called polymerase chain reaction (PCR), which analyzes DNA, has been increasingly used over the past decade to confirm whooping cough, which probably has increased the reporting of cases, Cherry said. The use of this test, for example, may have contributed to the difference between the number of pertussis cases reported during a 2005 outbreak in California and the reported cases in that state's 2010 outbreak, he said.
Still, even during the periods when cases were least frequent, pertussis outbreaks continued to occur every two to five years. That's because, unlike with measles and some other diseases, pertussis infections or vaccinations fail to give people lifelong immunity to the bacteria, Cherry said.
In addition, studies have shown that the DTaP vaccine provides less protection against the disease than did its predecessor, the DTP vaccine.
"Certainly the major epidemics in 2005, in 2010 and now in 2012 suggest that failure of the DTaP vaccine is a matter of serious concern," Cherry said.
It is possible instead that the bacteria that cause pertussis have undergone genetic changes, and some evidence has suggested links between such changes and the shortcomings of the vaccine, but the evidence is inconsistent, he said.
Better vaccines are needed, Cherry argued, but until they are found, use of the current vaccines needs to maximized. "Of particular concern are the frightening rates of complications and death associated with pertussis in unimmunized young infants," he said.
The strategy of "cocooning" infants, which means vaccinating the adults and children who are in regular contact with them, has shown some effectiveness, but the strategy is limited in its ability to curb cases of disease in infants. Currently, the first vaccine of the three-shot series that is given to babies is administered to 2-month-olds, but the schedule could be changed so that vaccinations begin at birth and the intervals between doses are briefer, he said.
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