The ORVAC trial: a phase IV, double-blind, randomised, placebo-controlled clinical trial of a third scheduled dose of Rotarix rotavirus vaccine in Australian Indigenous infants to improve protection against gastroenteritis: a statistical analysis plan

Abstract

Objective: The purpose of this double-blind, randomised, placebo-controlled, adaptive design trial with frequent interim analyses is to determine if Australian Indigenous children, who receive an additional (third) dose of human rotavirus vaccine (Rotarix, GlaxoSmithKline) for children aged 6 to < 12 months, would improve protection against clinically significant all-cause gastroenteritis.

Participants: Up to 1000 Australian Aboriginal and Torres Strait Islander (hereafter Indigenous) infants aged 6 to < 12 months will be recruited from all regions of the Northern Territory.

Interventions: The intervention is the addition of a third scheduled dose of human monovalent rotavirus vaccine.

Co-primary and secondary outcome measures: ORVAC has two co-primary outcomes: (1) anti-rotavirus IgA seroconversion, defined as serum anti-rotavirus IgA ≥ 20 U/ml 28 to 55 days post Rotarix/placebo, and (2) time from randomisation to medical attendance for which the primary reason for presentation is acute gastroenteritis or acute diarrhoea illness before age 36 months. Secondary outcomes include (1) change in anti-rotavirus IgA log titre, (2) time from randomisation to hospitalisation with primary admission code presumed or confirmed acute diarrhoea illness before age 36 months, (3) time from randomisation to hospitalisation for which the admission is rotavirus confirmed diarrhoea illness before age 36 months and (4) time from randomisation to rotavirus infection (not necessarily requiring hospitalisation) meeting the jurisdictional definition before age 36 months.

Discussion: A detailed, prospective statistical analysis plan is presented for this Bayesian adaptive design. The plan was written by the trial statistician and details the study design, pre-specified adaptative elements, decision thresholds, statistical methods and the simulations used to evaluate the operating characteristics of the trial. As at August 2020, four interim analyses have been run, but no stopping rules have been triggered. Application of this SAP will minimise bias and supports transparent and reproducible research.

Trial registration: Clinicaltrials.gov NCT02941107. Registered on 21 October 2016 ORIGINAL PROTOCOL FOR THE STUDY: https://doi.org/10.1136/bmjopen-2019-032549.

Keywords: Adaptive design; Bayesian; Infectious disease; Interim analysis; RV1; Randomised controlled trial; Rotarix; Rotavirus vaccine; Statistical methods.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Process flow diagram for interim analyses and decision rules

Fig. 2

Statistical power for clinical outcome for a range of baseline values, effect sizes and accrual rates

Fig. 3

Expected sample size (total enrolled) assessed on clinical and immunological outcome over a range of baseline values, effect sizes and accrual rates

Fig. 4

Statistical power for immunological outcome for a range of baseline values, effect sizes and accrual rates

Fig. 5

Probability of expected success assessed on clinical outcome over a range of baseline values, effect sizes and accrual rates

Fig. 6

Probability of futility assessed on clinical and immunological outcome over a range of baseline values, effect sizes and accrual rates

Fig. 7

Probability of stopping venous sampling assessed on immunological outcome over a range of baseline values, effect sizes and accrual rates

Fig. 8

Expected sample size (venous samples) assessed on immunological outcome over a range of baseline values, effect sizes and accrual rates