Vaccine and Immunotherapy Technologies

9-11 April 2008, Canberra

Dr John Clemens

Director General, International Vaccine Institute, Seoul, Korea

John Clemens is an international expert on the evaluation of vaccines in developing countries. He obtained an undergraduate degree from Stanford University and a masters and post-doctoral research training in clinical epidemiology at Yale University. From 1983 to 1988, he served as a research scientist at the International Centre for Diarrhoeal Disease Research in Bangladesh. On his return to the US, John served as Chief of the Epidemiology Section of the Center for Vaccine Development of the University of Maryland, and then as Chief of the Epidemiology Branch of the National Institute of Child Health and Human Development, at the US National Institutes of Health (NIH). While at NIH he was the Director of the first WHO Collaborating Centre for Vaccine Evaluation in Developing Countries. In 1999 he became the first Director-General of the IVI, a position he continues to hold. During his term, the IVI has established field research programs on vaccines and vaccine safety in 22 developing countries. John’s research focuses on evaluating vaccines in developing country populations, and on generating evidence for policy decisions about vaccine introduction in developing countries.

 

New approaches to the assessment of vaccine herd immunity and herd protection: Implications for future trials of vaccines against enteric infections

[Transcript of presentation not available]

Some vaccines can confer protection to populations that is greater than that expected on the basis of the proportion of the population vaccinated and the protective efficacy of the vaccine. These ‘indirect protective effects’ of vaccines in populations can occur via two different mechanisms: via ‘herd immunity’ and ‘herd protection’.

Indirect effects can increase the number of cases prevented per vaccinated individual in a population and improve its cost-effectiveness. Where direct effects are only moderate in magnitude, indirect effects can enhance protection to a level at which the vaccines can become potent tools for controlling disease. Since vaccination rates rarely reach 100%, these indirect effects may be critical to efforts to eradicate disease.

Traditionally, indirect protective effects of vaccines have been assessed only after vaccines have been licensed and deployed in public health practice. However they can also be measured in pre-licensure efficacy trials. Two approaches for such pre-licensure assessments have been used, one focusing on trial design and the other focusing on trial analysis. Both strategies should find greater use in the future.

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