LOS ANGELES - Successful booster vaccination of adolescents and adults against pertussis could have a significant impact on disease incidence. Elimination could be possible, according to James D. Cherry, MD, University of California, Los Angeles, School of Medicine.
"I'm an optimist. There's bits of information that say it's not possible; on the other hand, diphtheria was eliminated and the vaccine for diphtheria is no better than the pertussis vaccines," he said. "If we can do our job in pediatrics and do a significant amount in adults, we may be able to stop the circulation. You don't have to stop infection to stop circulation. You have to stop illness.
"If protection only lasts a few years, it won't happen. If it lasts reasonably well for 10 years, then I think it's possible," said Cherry, professor of pediatrics, UCLA division of pediatric infectious diseases.
Pediatricians have known for decades that hospitalized infants have frequently gotten pertussis from adults with cough illness unrecognized as pertussis, but only recently has this idea received widespread attention, Cherry said.
"It's been known to us for 20 years," he continued. "But, nobody really was totally aware of the situation."
Before pertussis was recognized as an adult problem, it was understood that natural infection with Bordetella pertussis provided life-long immunity; those who were vaccinated were thought to have only limited protection: "In fact, you're probably not protected as well from disease as from vaccination."
When pertussis was epidemic, Cherry explained, people were reinfected frequently, but their illness was mild and, therefore, not recognized.
"It's only now when we've had a chance to study people with cough illnesses that we find a significant number of pertussis cases in adults," he said. "Pertussis in adults begins as a mild illness, and by the time they seek care it's too late to get a positive culture."
Cherry stressed that although more cases of adult pertussis are now being reported, the increase should not be attributed simply to waning vaccine immunity, but also to increase awareness of the disease.
The challenge, if an adult formulation of pertussis vaccine is approved by the Food and Drug Administration, would be acceptance and willingness for vaccination by adults, he said.
"We don't do well with influenza. We haven't done well with tetanus. But, we did do well with tetanus and diphtheria when diphtheria was a problem," he said. "The good news is we can get in a sixth dose to adolescents [during the adolescent visit] and that will be a pediatric indication - and I'm sure we will be successful with that."
Cherry said that immunizing adults may be possible if given with a diphtheria and tetanus toxoid, but that more studies showing morbidity from pertussis in adults must first be conducted.
"We've got a long way to go on this, but we've come a long way in just six years," Cherry said.
The National Institutes of Health (NIH) Vaccine Treatment Evaluation Unit efficacy study is currently being conducted using an adult formulation of SmithKline Beecham's three-component DTaP vaccine (Infanrix).
The booster vaccine used in the study is roughly one-third of the pediatric dose, Cherry said, because adults get a good boost within two weeks of vaccination. Increasing the dosage would increase length of immunity, but would also increase local reactions, he added.
Preliminary results of the study have shown no significant difference in reactogenicity among adults and infants given the vaccine. Over 2,000 adolescents and adults will be enrolled and the participants will be monitored for more than two years to evaluate the vaccine's safety and efficacy.
Volunteers participating in the double-blind, placebo-controlled trial are randomized to receive either pertussis vaccine or hepatitis A vaccine as a control. Study participants are monitored bi-weekly for 12-18 months and detailed microbiologic and serologic tests are performed if a participant becomes ill and has a cough for five days or more, according to NIH.
You can express your views on this article, or other relevant themes, in the Infectious Diseases in Children Specialty Forums.