Monitoring the impact of vaccines postlicensure: new challenges, new opportunities.

Although vaccines are studied intensively before licensure, insight into important aspects of vaccine performance and the effectiveness of immunization programs and policies can only be detected after vaccines enter widespread use. Now that 17 diseases are targeted for prevention through routine immunizations in the USA, reassessment of the nation's vaccine-preventable disease-monitoring efforts is appropriate. Postlicensure disease monitoring has permitted recognition of indirect protection, vaccine effectiveness of various schedules, duration of protection, health disparities, importation patterns and microbial adaptation. The investments in vaccine research, development and regulatory procedures prelicensure, as well as resources devoted to purchase, distribution and delivery of vaccines after introduction, necessitate strategic efforts to monitor the impact of large-scale use of vaccines on disease over time.