Here is the design of a clinical trial:

Official Title: The ORVAC Trial: A Phase IV, Double-blind, Randomised, Placebo-controlled Clinical Trial of a Third Scheduled Dose of RV1 Rotavirus Vaccine in Australian Indigenous Infants to Improve Protection Against Gastroenteritis

Included conditions:
- Viral Gastroenteritis Due to Rotavirus

Study Armgroups:
- {'label': 'Rotarix', 'type': 'EXPERIMENTAL', 'description': 'Rotarix (RV1) vaccine, 1mL liquid suspension administered orally.', 'interventionNames': ['Drug: Rotarix (RV1)']}
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'Placebo liquid suspension manufactured to mimic Rotarix (RV1) vaccine, 1ml administered orally', 'interventionNames': ['Drug: Placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'Rotarix (RV1)', 'description': 'ROTARIX™ (RV1) is a live-attenuated human monovalent oral vaccine containing attenuated G1P\\[8\\] human rotavirus strain sponsored and distributed in Australia by GlaxoSmithKline Biologicals where it is licensed for the prevention of rotavirus gastroenteritis.', 'armGroupLabels': ['Rotarix'], 'otherNames': ['ROTARIX™']}
- {'type': 'DRUG', 'name': 'Placebo', 'description': 'The placebo for this trial will be Viscosweet, a clear and flavoured solution used as a pharmaceutical excipient repackaged into a labelled syringe identical to the active and firmly sealed with an end cap.', 'armGroupLabels': ['Placebo'], 'otherNames': ['Viscosweet']}

Primary Outcomes:
- {'measure': 'Time from randomisation to medical attendance for acute gastroenteritis or acute diarrhoea illness', 'description': 'Time from randomisation to medical attendance (hospitalisation, emergency department presentation, medical clinic presentation) for which the primary reason for presentation is presumed or confirmed acute gastroenteritis or acute diarrhoea illness between randomisation and age 36 months.', 'timeFrame': 'Randomisation to 36 months'}
- {'measure': 'Occurrence of anti-rotavirus IgA seroconversion', 'description': 'Anti-rotavirus IgA seroconversion, defined as serum anti-rotavirus IgA \\> 20U/ ml 28 to 55 days post RV1/placebo among infants with anti-rotavirus serum IgA \\< 20U/ ml before RV1/placebo, to be summarised as the proportion of all children per group.', 'timeFrame': '28-55 Days post RV1/placebo administration'}

Please estimate the sample size based on the assumption: 
The analyses will be conducted within a Bayesian framework. Interim analyses will occur after every 50th child enrolled or every 3 months, with the first interim analysis at 70 participants. The clinical endpoint analysis will start at 200 participants. The trial will stop for futility if there is a very low chance of observing a greater proportion of seroconversion or median time to medical attendance in the treatment arm. The trial will stop for expected success if the probability of higher seroconversion or median time to event in the treatment arm exceeds a threshold controlling type I error.
Data analyses and sample size
        Participant demographics and baseline characteristics will be summarised and tabulated by treatment group and location of residence. For the immunological endpoint, multivariate logistic regression will be used to compute the logs odds of the treatment effect. For the clinical endpoint, a Weibull parametric survival model will be used to compute the treatment effect, obtaining an absolute measure of median time to medical attendance in each arm. All analyses will occur within a Bayesian framework.
        In addition to modelling the treatment effects, we will include parameters to account for locality of residence, breastfeeding status in the 7 days prior to randomisation and, where applicable, indicator variables for gastroenteritis outbreaks.
        Secondary endpoints will be analysed using the same methods. Hypotheses, methods, prior distribution specification and probability thresholds that are alluded to here but omitted for brevity and accessibility will be detailed in a separately published statistical analysis plan.
        The first interim analysis will occur when 70 participants have immunogenicity results available. Further interim analyses will occur after every subsequent 50th child is enrolled or after every 3 months, whichever occurs sooner. If fewer than 25 children are enrolled in the 3-month interval, then the analyses will be deferred until the next scheduled interim. Analysis of the clinical endpoint will start when 200 children are enrolled in order that there are enough events to meaningfully undertake a time to event analysis. At each interim analysis, we will independently estimate:
        
          
            The posterior probability that the proportion of children achieving an IgA seroconversion in one arm is greater than in the other arm.
          
          
            The posterior probability that the median time to first medical attendance is greater in one arm than in the other arm.
          
        
        To assess futility, we will compute the predicted probability of trial success in both endpoints as if all resources were fully expended. If there is a very low chance of observing a greater proportion of seroconversion in the treatment arm OR there is very low chance of observing a greater median time to medical attendance in the treatment arm, then the trial will be stopped. Futility can be determined based on the results from either the immunological or the clinical endpoint. If futility is not concluded, we will then evaluate (1) whether the treatment arm has a higher rate of seroconversion compared with the placebo arm, and (2) whether a treatment effect is apparent in the clinical endpoint.
        If the probability that the rate of seroconversion in the Rotarix group is higher than in the placebo group, above a threshold level chosen to control the type I error, then we will cease collecting blood samples. Enrolment into the trial will continue, as will interim analyses, in order to assess the clinical endpoint until a decision rule is triggered for expected success or futility, or until we reach the maximum sample size of 1000 participants. If 250 infants with immunogenicity results have been enrolled without the above stopping rules having been met, no further venous blood samples will be collected.
        If the probability that the median time to event in the Rotarix group is greater than in the placebo group, above a threshold level chosen to control the type I error, then we will cease enrolment into the trial for expected success. We will continue to process any outstanding immunological results and follow patients up to 36 months old at which point we will undertake the final analysis and publish our findings. We note that expected success can only be determined based on the clinical endpoint.
        After 1000 infants have been enrolled without meeting a trial stopping rule, no further participants will be enrolled. Regardless of whether the trial is ceased for superiority or futility or continues to the maximum sample size, we will complete a final analysis once all follow-up data have been received.
        With the necessary governance and ethics approvals, access will be granted to the full protocol, Statistical Analysis Plan (SAP), analysis code and final dataset to allow for independent validation of the analysis.