How valid are IMS DA summary statistics of children's vaccination status?

Accurate recording of immunization status is essential for the evaluation of any immunization programme. In September 2006, 7-valent pneumococcal conjugate vaccination (PCV7) was introduced into the UK's routine childhood immunization programme. This study validated the PCV7 immunization status of children aged 2 years recorded in the IMS Disease Analyses (DA) database.

The PCV7 vaccination uptake rate for children born in 2008 in the IMS DA database was calculated. A sample of 173 of the 2497 children not recorded as vaccinated was identified, and a questionnaire was sent to each of their general practitioners to ascertain the child's true PCV7 vaccination status.

In the IMS DA data of 15 237 children born in 2008, 12 740 (83.6%) had a vaccination record of PCV7. One-hundred and eleven of the 167 questionnaires sent to the child's general practitioners were returned, giving an adjusted response rate of 111/167 (66.5%). Based on the general practitioners' responses, 71 (64%) of these children were fully vaccinated according to their general practitioner's records making the revised estimated vaccination rate for this cohort 94.1% CONCLUSION: This validation study has shown that caution is needed if using historical IMS patient-level data to analyse the effectiveness of PCV7 as there is a potential under-recording of immunization leading to under representation of vaccination rates by approximately 10%. Copyright © 2016 John Wiley & Sons, Ltd.