J Med Ethics 38:619-625 doi:10.1136/medethics-2011-100145
  • Papers
    • Research ethics

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

  1. for the Vaccine Assessment Using Linked Data (VALiD) Working Group*
  1. 1Discipline of Public Health, University of Adelaide, Adelaide, South Australia, Australia
  2. 2Discipline of Paediatrics, University of Adelaide, Adelaide, South Australia, Australia
  3. 3School of Population Health and Clinical Practice, University of Adelaide, Adelaide, South Australia, Australia
  1. Correspondence to Jesia G Berry, Discipline of Public Health, University of Adelaide, Level 6, Bice Building, Royal Adelaide Hospital, Mail Drop DX650 511, Adelaide, South Australia, Australia; jesia.berry{at}
  1. Contributors MG, AB-M and PR made substantial contributions to the conception and design of the study and obtained funding for the project. KD was the trial coordinator and led the design and direction of the study and application for ethical approval. JB and KD developed and piloted the study invitation material and telephone survey, and MG, AB-M and PR contributed to the design elements. PR designed the statistical analysis for the trial. JB developed the trial protocol, conducted interviews, collected and analysed the data, and wrote the first draft of the manuscript. All authors contributed critical revisions to the manuscript. Vicki Xafis contributed to the design elements of the study mail-outs and survey. Catherine Leahy developed the database management system and Jillian Edwards (Health Informatics, Policy and Performance Outcomes Unit (HIPPO), CYWHS) provided births data. Dr Val Edyvean (Registrar), Mr Darren Shaw and Mr Ian Neale (staff affiliated with the Births, Deaths and Marriages Registration Office) facilitated weekly screenings of infant and maternal deaths. Tina Evans (Departmental Secretary at the Discipline of Paediatrics) ordered medical records for clerical review and facilitated data exchange. Lisa Yelland, Katherine Lee and John Carlin provided helpful statistical advice regarding multiple imputation.

  • Received 28 July 2011
  • Revised 2 February 2012
  • Accepted 25 March 2012
  • Published Online First 19 April 2012


Introduction No consent for health and medical research is appropriate when the criteria for a waiver of consent are met, yet some ethics committees and data custodians still require informed consent.

Methods A single-blind parallel-group randomised controlled trial: 1129 families of children born at a South Australian hospital were sent information explaining data linkage of childhood immunisation and hospital records for vaccine safety surveillance with 4 weeks to opt in or opt out by reply form, telephone or email. A subsequent telephone interview gauged the intent of 1026 parents (91%) in relation to their actions and the sociodemographic differences between participants and non-participants in each arm.

Results The participation rate was 21% (n=120/564) in the opt-in arm and 96% (n=540/565) in the opt-out arm (χ2 (1 df) = 567.7, p<0.001). Participants in the opt-in arm were more likely than non-participants to be older, married/de facto, university educated and of higher socioeconomic status. Participants in the opt-out arm were similar to non-participants, except men were more likely to opt out. Substantial proportions did not receive, understand or properly consider study invitations, and opting in or opting out behaviour was often at odds with parents' stated underlying intentions.

Conclusions The opt-in approach resulted in low participation and a biased sample that would render any subsequent data linkage unfeasible, while the opt-out approach achieved high participation and a representative sample. The waiver of consent afforded under current privacy regulations for data linkage studies meeting all appropriate criteria should be granted by ethics committees, and supported by data custodians.

Trial registration number Australian New Zealand Clinical Trials Registry ACTRN12610000332022.


  • * Members include: University of Adelaide, SA: Michael S Gold, Annette J Braunack-Mayer, Philip Ryan, Katherine M Duszynski, Jesia G Berry, Vicki Xafis, Jillian Carlson, Bernadette Richards and Jackie M Street. New South Wales Department of Health, NSW: Lee K Taylor. Royal Children's Hospital, Vic: Jim P Buttery. University of Melbourne, Vic: Cecily J Freemantle. Monash University, Vic: John J McNeil and Lisa L Demos. University of Wollongong, NSW: Colin Thomson. University of New South Wales, NSW: Glenda L Lawrence. The University of Sydney, NSW: Elizabeth J Elliot and Julie Leask. John Hunter Hospital, NSW: Rod Givney. Therapeutic Goods Administration, ACT: Gary Lacey. SA Health, SA: Tony Woollacott, Chris Gascoigne, Ann Koehler, Maureen Watson, Rebecca Horgan and Sarah Lawson. University of Western Australia, WA: Peter C Richmond. Medicare Australia, ACT: Sean Tarrant. University of South Australia, SA: Elizabeth E Roughead.

  • Funding This work was supported under the Australian Research Council (ARC) Linkage Projects funding scheme (project number LP0882394). MG, AB-M, PR, John McNeil, Jane Freemantle, Colin Thomson, Elizabeth Roughhead, Lee Taylor and Jim Buttery are Chief Investigators on this grant. Lee Taylor, David Filby, Jim Buttery and Elizabeth Elliot are Partner Investigators affiliated with organisations who provided financial and/or in-kind support: the South Australian and New South Wales Departments of Health (SA Health and NSW Health), Surveillance of Adverse Events Following Vaccination in Victoria (SAEFVic) at the Royal Children's Hospital in Victoria; and the Australian Paediatric Surveillance Unit (APSU) at the Children's Hospital at Westmead in NSW.

  • Competing interests None.

  • Patient consent In the trial, all eligible subjects were included without their consent to avoid introducing selection bias in the study sample. The local institutional HREC granted a waiver of the usual requirement for consent and allowed the limited disclosure to subjects of the true purpose of the trial.

  • Ethics approval Children, Youth and Women's Health Service (CYWHS) Human Research Ethics Committee (reference number: REC2087/7/11).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The authors are willing to share anonymised data for the trial, available on request from the corresponding author and subject to ethical approval of data release by the Women's and Childrens Health Network (WCHN) Human Research Ethics Committee (HREC) (formerly the Children, Youth and Women's Health Service HREC).

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