INTRODUCTION: The mHealth active participant centred (MAPC) adverse events following immunisation (AEFI) surveillance is a promising area for early AEFI detection resulting in risk minimisation. Passive (spontaneous) AEFI surveillance is the backbone for vaccine pharmacovigilance, but has inherent drawbacks of under reporting, and requires strengthening with active surveillance methods. AIM: The Zimbabwe stimulated telephone assisted rapid safety surveillance (Zm-STARSS) randomised controlled trial (RCT) sought to evaluate the efficacy and feasibility of AEFI detection using a short message service (SMS) and computer assisted telephone interview (CATI) approach. METHOD: A multicentre Zm-STARSS RCT enrolled consented adult vaccinees or parents or guardians of children receiving vaccines, including COVID-19 vaccines, at study vaccination clinics. At enrolment study participants were randomised to either SMS-CATI group or control group. SMS prompts were sent on days 0-2 and 14 post-vaccination to SMS-CATI group to ascertain if a medically attendance or attention due to an Adverse event following immunisation (AEFI) had occurred. However, no SMSs were sent to the control group. SMS-CATI group who responded "Yes" to SMS prompts were interviewed by research healthcare workers (RHCWs) who completed a CATI to determine if an AEFI had occurred whilst an AEFI in control group was determined from passive AEFI reporting channels. The primary study outcome was the AEFI detection rate in the SMS-CATI group compared to the control group. RESULTS: A total of 4560 participants were enrolled after signed informed consent, all were encouraged to report AEFIs and randomised automatically on 1:1 basis into two arms SMS CATI intervention group (n = 2280) and a control passive AEFI surveillance group (n = 2280) on day 0. A total of 704 (31 %) participants responded to the SMS prompts, with 75 % (528/704) indicating "No" and 25 % (176/704) reporting "Yes" to seeking medical attention or attendance post-immunisation. 69 % (121/176) completed a CATI survey but in only 36 % (44/121) was the AEFI confirmed. There were no AEFIs reported in control group participants. The detection rate of a AEFI associated with medically attendance or attention using the SMS-CATI methodology was 2 % (44/2280) on an intention to treat cohort. CONCLUSION: Despite the low SMS response and CATI completion rate, we demonstrated that Zm-STARSS SMS system improves AEFI detection compared to passive AEFI surveillance. We recommend that this and similar approaches are explored further using cost-effective multi-channel digital approaches for holistic pharmacovigilance to improve AEFI detection in Low Middle-Income Countries (LMICs) for all vaccines.