Development, acceptance, and use of immunologic correlates of protection in monitoring the effectiveness of combination vaccines.

The establishment of immunologic correlates of protection for all vaccine antigens is a worthwhile goal. It allows new vaccines to be licensed on the basis of attainment of defined immunologic benchmarks, without the need for large-scale efficacy trials for each new product. This is particularly important for the evaluation of new combination products. Efficacy trials of each new mixture would be unethical because routinely recommended vaccines would be denied children in the control group. The establishment of immunologic correlates of protection should be a defined goal of every efficacy trial. Additional ways to evaluate the immune responses-such as cell-mediated immunity, mucosal immunity, memory responses, and antibody avidity-should also be studied. Finally, ongoing surveillance efforts are also needed, to monitor the impact of new and combined vaccines on disease rates.