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Teens to be the target of pertussis boosters

More frequent outbreaks of the disease are leading to heightened awareness and are raising concerns in the public health community.

By Susan J. Landers, amednews staff. Oct. 6, 2003. - Clarification

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Washington -- Pertussis is believed by many to be a disease of young children. However, sometimes a lengthy bout of a severe, hacking cough in an adolescent or adult patient should trigger suspicion, too.

It's a critical awareness for primary care physicians because the consequences of missing a pertussis diagnosis could be serious, even fatal, for unvaccinated infants who come in contact with these individuals.

"We in peds tend to think about pertussis, but I don't think the adult folks do. I think there is probably a lot of underdiagnosis going on in family practitioner and internal medicine offices," said Margaret Rennels, MD, professor of pediatrics at the University of Maryland Medical School.

Vaccine schedules call for the first shot of the DTaP vaccine series to be given to infants when they are 2 months old with the fifth, final dose generally administered by age 6 years.

Although adolescents and adults who develop pertussis are more likely to get a milder disease, the hazard is that they are the parents, uncles and aunts of infants and could transmit the disease.

"So although it doesn't mean too much to the adolescents and adults in terms of illness, in terms of public health they are important because they turn out to be the spreaders, and they bring it home," said William Schaffner, MD, chair of the Dept. of Preventive Medicine at Vanderbilt University Medical Center, Nashville, Tenn.

There is still some debate over whether there is a real increase in pertussis or whether it is a matter of the disease being better recognized and diagnosed, noted Rennels. "But the current thought is that it is probably real."

Pertussis outbreaks are not unusual, said Kris Bisgard, DVM, MPH, a medical epidemiologist at the Centers for Disease Control and Prevention. The outbreaks occur when there are enough susceptible people -- something that happens naturally because the i mmunity imparted by the vaccine wanes over time.

"Even in the best of circumstances, like after the fourth dose is given, the vaccine is only about 85% effective against severe pertussis," said Dr. Bisgard. However, it is generally recognized that the vaccine does protect against death and that fully vaccinated children are well-protected. (See clarification.)

The way the body develops and expresses the vaccine's protection against pertussis is not completely understood, said Dr. Schaffner. "For other vaccines we know exactly what to measure in the blood stream that correlates with immunity; for pertussis we are still trying to figure that out."

Pertussis boosters

The fact that the vaccine has to fight a bacterial infection seems to make pertussis a more formidable opponent than a virus-caused disease like measles, said Dr. Bisgard.

The CDC's Epidemic Intelligence Service recently investigated a pertussis outbreak in South Carolina. There was some thought that the outbreak was caused by a new strain of pertussis, but that proved not to be the case, at least so far.

Meanwhile, a booster shot for pertussis is likely in the near future for adolescents. Although a suitable vaccine for this older age group is not yet licensed, a couple are in the works, said Dr. Rennels. "When they are licensed, I wouldn't be surprise d if a booster is recommended," she said.

Aventis Pasteur expects to submit its adolescent and adult version of the acellular pertussis vaccine to the Food and Drug Administration for approval soon with a likely approval by 2005, said Michael Decker, MD, MPH, vice president for scientific and medical affairs at Aventis.

Dr. Decker expects the vaccine to first target 12-year-olds because their original vaccinations, at age 6, are likely wearing off.

If the United States does move toward pertussis boosters, it will be a road already taken by Canadians. In August, the Canadian Pediatric Society recommended that all provinces provide a booster shot of acellular pertussis vaccine to adolescents. So fa r, only a few provinces and the Northwest Territories routinely administer the boosters.

Although the Canadian health system doesn't yet cover the cost of the boosters, the pediatric society is recommending that physicians discuss the risks and benefits of the vaccine with adolescents and their parents so they may make an informed decision about whether to pay for the shots themselves.

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