Our study was one of the first acellular-pertussis vaccine studies in India to be published in a peer- reviewed journal. Reactogenicity of diphtheria- tetanus-pertussis vaccines have largely been attributed to whole-cell pertussis components, and are significantly reduced in similar combination acellular pertussis vaccines(1). Reactions increase with age: A driver for the development of acellular-pertussis vaccines was the unsuitability of whole-cell vaccines to boost older persons(2).

Our study vaccine included a low-dose pertussis component, specifically for boosting, comprising approximately 33% of the antigen content in DTPa priming vaccines. This is possible without compromising protection because an immunogenic response from a primed immune system requires less antigen concentration than a naïve system. Hence, the likelihood of vaccine adverse reactions is reduced further.

Therefore, despite any similarity in proportions suffering reactions, it is not appropriate to compare our results with those of any studies involving infants. The incidence of reactions one would have expected using whole-cell pertussis vaccines in pre-schoolers is significantly greater than that observed in our study. This has been confirmed in head-to-head studies, comparing the booster formulation vaccine against a diphtheria-tetanus-whole cell pertussis vaccine in pre-schoolers: there was a highly significant difference in reactogenicity (P <0.001) in favour of the booster vaccine(1). In our experience, the lack of a single reported case of high fever (>39.1°C) in a clinical study of pre-schoolers given any pertussis vaccine (as observed in our study) is unique in India. Additionally, the Thai and Israeli studies referenced in our paper found no compromise in diphtheria or tetanus protection in pre-schoolers, despite the lowered diphtheria and tetanus toxoids antigen contents.

The booster vaccine is gaining global acceptance (including in Europe and North America) for use in all age groups above the age of 4 years, with the data indicating non-inferiority when used as a booster for protection against diphtheria-tetanus and pertussis, compared to available alternatives(4). An Indian Academy of Paediatrics publication states it may be used in pre-schoolers and is preferred after age 7 years(5). We believe the good safety and reactogenicity profile demonstrated in our study will help the vaccine contribute to the control of diphtheria and pertussis in India.

S.K. Datta,
A.P. Dubey*,
*Maulana Azad Medical College,Delhi
and
GSK Biologicals, Belgium.
E-mail: [email protected]