Diphtheria, tetanus and pertussis
Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Infanrix (SmithKline Beecham)
0.5 mL glass vials
Despite the availability of triple antigen, there has been an epidemic of whooping cough in Australia. Concern about the safety of the pertussis component of the vaccine may be contributing to the inadequate immunisation of Australian children.
The current pertussis component of triple antigen is a whole-cell vaccine. This is thought to be responsible for the frequent adverse effects such as irritability, crying, fever and injection-site reactions. The new product aims to stimulate immunity while reducing the incidence of adverse reactions.
The pertussis component of this product contains 3 purified antigens of Bordetella pertussis. Although it is not a whole-cell vaccine, it induces antibodies in over 95% of children given a 3-dose course.
Two types of a cellular vaccine have been tested in a double-blind trial involving over 14 000 children.1 At 2,4 and 6 months of age, they were given either diphtheria and tetanus toxoid, triple antigen including whole-cell pertussis, or triple antigen containing one of two brands of a cellular pertussis vaccines. The acellular vaccines had a much higher immunogenicity than the whole-cell vaccine and appeared to be more effective. After a mean follow-up of 17 months, 37 cases of pertussis occurred in the 4481 children who had received this product compared with 141cases in the 4348 who had received whole-cell vaccine. The children who had received whole-cell vaccine were also significantly more likely to have adverse effects. The frequency of adverse events in children given the a cellular vaccines was similar to those given diphtheria and tetanus toxoids.
In addition to primary courses of immunisation, this product has also been successfully used as a booster at 18 months or 4-6 years. It is effective and has been approved for this indication, including children who were originally immunised with the whole-cell vaccine.
The new vaccine is likely to be effective against the serotypes of Bordetella pertussis currently found in Australia. On the available data, it appears to be safe in the short term and has advantages over whole-cell vaccine. The health economists will have to calculate if these advantages outweigh the cost of the new vaccine.