assembles and maintains its computerized files on a secure server at the site. This distributed data model has permitted the creation of dynamic data files that permit the ongoing capture of near real-time event-based MCO administrative data. These include data on vaccinations, hospitalizations, emergency department and clinical care visits, and certain demographic characteristics. While most files are updated weekly with new data from each MCO, some files are updated less frequently (Baggs et al., 2011). This organization of the data enables near real-time postmarketing surveillance to be conducted and enhances the timeliness of certain studies.
Surveillance and Research
The VSD has been used to conduct rigorous epidemiological studies on a wide range of immunization safety topics. Strategic priorities for research and surveillance are developed and updated regularly. The following priorities were reported in 2011 (Baggs et al., 2011):
The enhancements in data transfer and updating permit near real-time postmarketing surveillance. Adverse events identified in the VSD system are analyzed by use of an active surveillance system called Rapid Cycle Analysis. Every week, the Rapid Cycle Analysis team determines the rates of adverse events associated with newly licensed or recommended vaccines in the study population. This information allows VSD researchers to compare the rates of adverse events in similar groups of people to determine if an event is related to the vaccine. If an increased risk is detected, VSD project scientists implement a formal, population-based epidemiological study to test the hypothesis of a causal relationship.
VSD data are also used in conjunction with data from VAERS to determine, for example, whether the number of adverse events reported to VAERS exceeds the background occurrence of the events shown in VSD.
VSD has been used to conduct rigorous studies on a wide range of topics on vaccine safety, as well as studies on immunization coverage, disease incidence, research methodologies, cost-effectiveness, and medical informatics (Baggs et al., 2011; DeStefano, 2001). For example, VSD has been used to study immunization safety concerns, such as the risk of seizures following receipt of the whole-cell pertussis vaccine or the measles, mumps,