Strategies to Maximize Participant Retention in the Sierra Leone Trial to Introduce a Vaccine Against Ebola (STRIVE)

Abstract

Background. STRIVE, a phase 2/3 trial of investigational rVSVΔG‐ZEBOV (Merck) vaccine was implemented in 5 districts in Sierra Leone during the 2014‐ 2015 Ebola epidemic. Eligible health care workers and front line Ebola response workers were individually randomized to immediate (within 7 days) or deferred (within 18‐ 24 weeks) vaccination and followed for 6 months after enrollment or vaccination for medical events, including Ebola virus disease (EVD). There were concerns that high rates of follow‐up would be difficult to achieve in a low resource setting with poor communications infrastructure. Methods. The study design incorporated several features to maximize participant retention, especially for the deferred vaccination group. To facilitate safety follow‐up, STRIVE provided cell phones to participants with free calls to study staff and a dedicated hotline for participants to report health concerns and be referred for clinical care. Trial staff conducted monthly calls to participants using their study phone or personal/ other phone number if provided, making up to six attempts. Home visits were made if participants could not be contacted by phone. Preliminary follow‐up data are presented. Results. Of the approximately 8650 participants enrolled and randomized, half were assigned to the immediate vaccine group and half to the deferred group. Approximately 1% withdrew or were lost to follow‐up within 6 weeks of vaccination (immediate group) or enrollment (deferred group). About 95% of the immediate vaccination group completed 6 months of safety follow‐up, and 88% of the deferred vaccination group completed pre‐vaccination follow‐up and were vaccinated. Postvaccination follow‐up in the deferred group is ongoing. The most common reasons for early termination were declining deferred vaccination followed by losses to follow‐ up. To date, no vaccine‐related serious adverse events or EVD cases have been reported. Conclusion. High retention of study participants in a vaccine clinical trial in a low resource setting was achievable using multiple follow‐up methods. Use of a deferred intervention control group in the design of a randomized clinical vaccine trial in an outbreak in such a setting is feasible.