Does the National Immunisation Register stack up? Quantifying accuracy when compared to parent-held health record books.

Aim: The National Immunisation Register (NIR), which is derived from general practice management systems, is an important tool for the provision of clinical services, national immunisation programme evaluation and immunisation research in New Zealand. However, the accuracy of the NIR data has not yet been quantified. This study aimed to examine, describe and quantify the extent of discrepancy in the NIR compared to Well Child Tamariki Ora parent-held health record books (Health Books).

Method: Immunisation data for vaccinations given between birth and four years old for children born between 2006 and 2019 were compared between the Health Books and the NIR. Health Book records were used as the reference standard to calculate performance measures: sensitivity, specificity, positive and negative predictive values for the NIR.

Results: Overall, NIR performance was high: sensitivity ranged from 90% to 93%, specificity from 78% to 85%, the positive predictive value from 91% to 94% and the negative predictive value from 77% to 84%. NIR performance was higher for National Immunisation Schedule (NIS) vaccines compared with non-NIS vaccines.

Conclusion: This study indicates the NIR data accuracy generally performs well compared with international equivalents, especially for NIS vaccine records. Further work is required to ascertain why discrepancies between the Health Books and NIR continue to occur, with particular attention to important subgroups and translating records across from migrant populations. Also, future work is required to understand the accuracy of vaccination records for groups who experience lower-quality healthcare and a higher burden of infectious diseases.