Monitoring vaccination coverage rates is important to the people of North Dakota, to public and private health-care providers and to government agencies. Maintaining high vaccination coverage helps protect all North Dakotans from vaccine preventable disease. With timely, detailed immunization data the ability of all stakeholders to coordinate effective vaccination strategies and help maintain high vaccine coverage rates is greatly increased. There are a variety of methods and surveys to measure vaccine coverage in North Dakota.
A widely used accepted source for immunization data is immunization information systems (IIS). IISs are confidential population based, computerized information systems that attempt to collect vaccination data for all persons within a state or geographical area. Ideally IISs provide supplemental data, such as local-level data and timely surveillance data, that other data collection methods cannot provide. IIS data also has limitations. First, an IIS is only as good as the data entered in the system. In North Dakota, health-care providers are required to enter child and adolescent data into the NDIIS, but adult vaccines are not required to be entered. Second, to determine a population denominator, the number of people in a geographic area, using the NDIIS can be difficult due to people moving in and out of different areas. As a result, the NDIIS tends to underestimate vaccination coverage compared to the National Immunization Survey (NIS).
The NIS are annual telephone surveys that provide current, population-based, estimates of vaccination coverage among children and teens. There are also limitations of NIS data. First, it takes a year to collect the target sample size per area and, as a result, NIS data are reported for the previous year leaving a gap between changes in the vaccine schedule and evaluation by the NIS. Second, the NIS is not designed to provide precise estimates for smaller geographic areas or for population subgroups within states.
The BRFSS is the world’s largest ongoing telephone health survey system, tracking health conditions and risk behavior in the US annually since 1984. For determining influenza vaccine coverage the BRFSS is one of the best methods. It has limitations in that it requires survey respondents to self-report vaccination coverage unlike the NIS that verifies immunization data with provider records.