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We read with interest the paper by Omenaas and colleagues1 on the relationship between tuberculin reactivity and the prevalence of atopy. The authors found no relationship between a positive tuberculin reaction and atopy, as assessed by IgE measurements, in this retrospective study of 20–44 year old adults who were BCG vaccinated at the age of 14.
However, we would like to comment on the design of the study and the interpretation of the data. Firstly, a long time elapsed between BCG vaccination and tuberculin testing. The mean age of the participants was 34 years, while BCG vaccination occurred at the age of 14. Only 60% of the subjects were positive tuberculin reactors 10 years after BCG vaccination in previous research, as stated by the authors. It is therefore possible that the tuberculin negative group contained a considerable number of initial responders to BCG vaccination (with subsequent lower IgE levels), thereby minimising the difference between the tuberculin positive and tuberculin negative groups.
Secondly, in our opinion the study by Omenaas et al suggests that modulation of the immune response by BCG vaccination at the age of 14 does not result in a reduction of atopy in adults. Based on their findings, the authors conclude that “host characteristics such as Th1/Th2 balance do not explain the relationship between tuberculin reactivity and atopy observed in the younger Japanese population2 and that this relationship may be limited to populations immunised in early childhood”. However, we think that the effect of BCG on the immune system in early childhood could be different and cannot be predicted by the study performed by Omenaas, since this study is not designed to do so. For this purpose a prospective randomised trial in young children is required.
authors' reply We thank Drs Steenhuis and Hoekstra for their comments on our cross sectional study indicating that modulation of the immune response by BCG vaccination at the age of 14 does not result in a reduction of atopy in adults. As pointed out in the paper, a long time elapsed between the BCG vaccination and tuberculin testing. Knowledge of the relationship between intraindividual immediate tuberculin reactivity after BCG vaccination and later reactivity is limited. However, our clinical experience tends to support the view that a person with a strongly positive reaction due to BCG vaccination will later show reactions that are weaker but of corresponding rank within the same cohort. We are not aware of data to support this view; there is, however, a possibility that the tuberculin negative group at follow up contained a high fraction of initial responders to the BCG vaccination (with subsequent lower IgE levels), thus minimising the difference between tuberculin positive and negative subjects. As pointed out by Drs Steenhuis and Hoekstra, this question can best be answered in a prospective randomised trial in young children.