Issues in selection of DTwP-based combination vaccines
Introduction
Combination vaccines, the best known of which is the traditional diphtheria–tetanus–(whole cell) pertussis (DTwP) vaccine, have been used for many years and offer several advantages, including a reduced number of injections, with a concomitant drop in syringe use and exposure to exipients, adjuvants and preservatives, and a non-disruptive way to introduce an additional antigen, such as hepatitis B (hep B) or Haemophilus influenzae type b (Hib) vaccines, into an immunization programme. Recent experience with DTwP-based combinations has attested to their enormous programmatic desirability. Despite their advantages, however, use of such combinations could limit programme flexibility and affect the supply of traditional vaccines. The purpose of this paper is to examine issues and implications surrounding the selection and use of DTwP-based combination vaccines. A summary of such vaccines currently available is given in Table 1.
The pros and cons of such combination vaccines are summarized in Table 2.
Section snippets
Regulatory issues
There are several special considerations for regulation of combination vaccines compared to a new single component vaccine. These include the need to demonstrate the safety and efficacy of each component in the combination, which may be difficult if there are no serological coordinates of immunity [1]. Furthermore, the response to each antigen in the combination may be adversely affected by interference with other components.
A special issue is the availability of continued regulatory oversight
Predictions for uptake
The available data allow the generation of a model to predict uptake of combination vaccines. This is shown in Table 4, where market characteristics are tabulated for different regions of the world and antigen uptake in the form of combination vaccines is predicted. Based on the knowledge we have to date, most of these predictions are upheld, as can be seen in Fig. 3, Fig. 4. This type of analysis can serve as a basis for long-term projections for future combination vaccines.
Lessons for the public health community
The current analysis supports strongly the concept that price alone is not the major predictor of uptake, especially for combination vaccines. Countries will pay a premium for an additional antigen in a combination only if it adds value. The value added for a particular antigen will differ across countries and regions, depending on epidemiological and other factors. The key is a real or perceived programmatic need, which can often offset vaccine price considerations. By adopting an approach
Acknowledgements
The authors would like to express their gratitude to Keeley Gyte, Gill Mayers, and the staff of the Vaccine Assessment and Monitoring Team of the WHO Department of Vaccines and Biologicals for providing the data in Fig. 3, Fig. 4, Fig. 5, and to Jay Wenger for reviewing the information therein.
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