Simulation via Instant Messaging-Birmingham Advance (SIMBA) delivers simulation-based learning through WhatsApp and Zoom, helping to sustain continuing medical education (CME) for postgraduate healthcare professionals otherwise disrupted by the coronavirus (COVID-19) pandemic. This study aimed to assess whether SIMBA helped to improve clinical knowledge and if this improvement in knowledge was sustained over time. Two SIMBA sessions-thyroid and pituitary-were conducted in July-August 2020. Each session included simulation of various real-life cases and interactive discussion. Participants' self-reported confidence, acceptance, and knowledge were measured using surveys and multiple-choice questions pre- and post-simulation and in a 6- to 12-week follow-up period. The evaluation surveys were designed using Moore's 7 Levels of CME Outcomes Framework. A total of 116 participants were included in the analysis. Significant improvement was observed in participants' self-reported confidence in approach to simulated cases (thyroid, n = 37, P < .0001; pituitary, n = 79, P < .0001). Significant improvement in clinical knowledge was observed following simulation (thyroid, n = 37, P < .0001; pituitary, n = 79, P < .0001). For both sessions, retention of confidence and knowledge was seen at 6-12weeks' follow-up. SIMBA increased participants' clinical knowledge on simulated cases and this improvement was retained up to 6-12weeks after the session. Further studies are required to explore long-term retention and whether it translates to improved real-world clinical practice.