Specific Biological Diagnoses Are Needed to Determine the Durability of Pertussis Vaccine–Induced Immunity

TO THE EDITOR—I believe that several issues should be discussed regarding the recent article by Witt et al [1]. The authors used only polymerase chain reaction (PCR) as a diagnostic method of pertussis without concomitant bacterial culture. They mention that their PCR was able to distinguish Bordetella pertussis from Bordetella holmesii by simply stating: “B. holmesii was unlikely to have been present in our population as there were no specimens positive for B. pertussis and B. parapertussis; a finding which should have been expected with B. holmesii infection due to amplification of both IS481 and IS1001 in B. holmesii.” However: 1. The target IS1001 is detected in the genome of Bordetella parapertussis and sometimes in the genome of Bordetella bronchiseptica but it is undetectable in the genome of B. holmesii with the technology used in the study. 2. The Cepheid technology can detect B. pertussis as well as B. holmesii if the IS481 probe is used, which is listed as B. pertussis specific in the publication [1]. 3. The authors should quote and discuss the data of Yih et al regarding an outbreak of pertussis in Massachusetts in 1999 [2], the data of Guthrie et al in Canada [3, 4], and the recent data of Njamkepo et al in France [5]. 4. In the Methods section the vaccine status of 3 groups of subjects is defined, but no information is given on how the undervaccinated children have been taken into account in the calculation of the vaccine's effectiveness. This information is important for all age groups, and even more so in those aged 2–7 years; within this group, undervaccinated children receiving a full primary series of vaccination, booster at 18 months, and no preschool booster were not comparable to children receiving the incomplete primary series, booster at 18 months, and no preschool booster. In conclusion, in the present study, the value of vaccine effectiveness per age group cannot be considered to be correct, as specific probes for the diagnosis were not used, in particular among adolescents. This is a major problem concerning the interpretation of the results and the message delivered. Epidemiological data should be published only if supported by strict coordination with experts in biological diagnosis.