SAN FRANCISCO — An analysis of a pertussis outbreak at a day care center in Israel revealed that the efficacy of the acellular pertussis vaccine in children who were vaccinated was 93%, Dr. Ellen S. Bamberger reported during a poster session at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy sponsored by the American Society for Microbiology.
“When we look at the distribution of children who actually got pertussis, the pertussis vaccine actually protects, and the children who are unvaccinated in an outbreak setting are much more likely to be infected, and their clinical symptoms tend to be more severe,” Dr. Bamberger of the B'nai Zion Medical Center in Haifa, Israel, said in an interview.
She and her associates investigated 31 children aged 3–5.5 years who were exposed to a child with pertussis at a day care center in Haifa. Parents of the children filled out questionnaires about symptoms and immunization status, and the researchers obtained nasopharyngeal swabs for Bordetella pertussis and polymerase chain reaction (PCR) testing that targeted the pertussis toxin.
They conducted follow-up exams at 21 days and obtained repeat samples in symptomatic children.
Of the 31 children, 6 (19%) tested positive for pertussis by PCR. Only 2 of the 27 children (7%) who had been vaccinated against the disease tested positive for pertussis, compared with each of the 4 children who had not received a vaccination (100%). Dr. Bamberger and her associates calculated the vaccine to be 93% efficacious.
Azithromycin chemoprophylaxis was recommended for all exposed children but only 15 of the 25 exposed children (56%) took azithromycin. The dose was 10 mg/kg on the first day followed by 5 mg/kg for 4 days.
At 21-day follow-up, 2 of the 6 children with laboratory-confirmed pertussis (33%) reported a mild residual cough and 5 of the 25 exposed children (20%) had developed an upper respiratory tract infection with cough. Three of these 5 children (60%) had completed azithromycin prophylaxis. There were no further cases of laboratory-diagnosed pertussis in any of the exposed children, regardless of whether chemoprophylaxis was taken or not.
“Chemoprophylaxis with azithro-mycin did not appear to afford any added benefit in thwarting the development of pertussis among recently vaccinated children exposed to a pertussis outbreak,” the researchers wrote in their poster.
“Our findings confirm the high efficacy and importance of the acellular pertussis vaccine in day care children, and despite the limited number of subjects in the study, raise questions about the added value of chemoprophylaxis in this age group.”