A randomised controlled trial to compare opt-in and opt-out parental consent for childhood vaccine safety surveillance using data linkage: study protocol

Trials. 2011 Jan 4:12:1. doi: 10.1186/1745-6215-12-1.


Background: The Vaccine Assessment using Linked Data (VALiD) trial compared opt-in and opt-out parental consent for a population-based childhood vaccine safety surveillance program using data linkage. A subsequent telephone interview of all households enrolled in the trial elicited parental intent regarding the return or non-return of reply forms for opt-in and opt-out consent. This paper describes the rationale for the trial and provides an overview of the design and methods.

Methods/design: Single-centre, single-blind, randomised controlled trial (RCT) stratified by firstborn status. Mothers who gave birth at one tertiary South Australian hospital were randomised at six weeks post-partum to receive an opt-in or opt-out reply form, along with information explaining data linkage. The primary outcome at 10 weeks post-partum was parental participation in each arm, as indicated by the respective return or non-return of a reply form (or via telephone or email response). A subsequent telephone interview at 10 weeks post-partum elicited parental intent regarding the return or non-return of the reply form, and attitudes and knowledge about data linkage, vaccine safety, consent preferences and vaccination practices. Enrolment began in July 2009 and 1,129 households were recruited in a three-month period. Analysis has not yet been undertaken. The participation rate and selection bias for each method of consent will be compared when the data are analysed.

Discussion: The VALiD RCT represents the first trial of opt-in versus opt-out consent for a data linkage study that assesses consent preferences and intent compared with actual opting in or opting out behaviour, and socioeconomic factors. The limitations to generalisability are discussed.

Trial registration: Australian New Zealand Clinical Trials Registry ACTRN12610000332022.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Data Collection* / statistics & numerical data
  • Health Behavior
  • Health Care Surveys
  • Health Knowledge, Attitudes, Practice*
  • Humans
  • Immunization Programs
  • Immunization Schedule
  • Infant
  • Medical Record Linkage
  • Parental Consent* / statistics & numerical data
  • Parents / psychology*
  • Population Surveillance*
  • Product Surveillance, Postmarketing* / statistics & numerical data
  • Research Design*
  • Single-Blind Method
  • Socioeconomic Factors
  • South Australia / epidemiology
  • Vaccines / adverse effects*


  • Vaccines