Background: Australian EDs have seen evidence of viral evolution over 5 waves of COVID-19 infection.

Objective: To describe the impact of the 6^th to 8^th regional waves of infection on the Canberra Hospital ED.

Methods: Cohort Study using prospectively collected data during 3 retrospectively identified waves of COVID-19: Wave 6 (21-Nov-22 for 9 weeks), Wave 7 (10-Apr-23 for 13 weeks) and Wave 8 (16-Oct-23 for 6 weeks and ongoing). Primary research questions were proportion of ED workload, frequency of incidental diagnoses and age distribution.

Results: Wave 6 consisted of 583 presentations (525 different patients), wave 7 of 664 (599) and wave 8 of 170 (156). The ratio of presentations to reported cases rose from 0.032 to 0.078 between wave 6 and 7, when reporting became non mandatory, but fell to 0.39 in wave 8. The proportion of ED presentations with active COVID fell from 3.83% (95%CI 3.53-4.15) in wave 6 to 2.87% (2.66-3.10) in wave 7 to 1.44% (1.24-1.68) in wave 8. There was no significant difference between the proportion of incidental COVID cases in each wave, average 41.6%. The proportion under 5 years increased from 12.5% (10.0-15.5) in wave 6 to 22.4% (19.4-31.9) in wave 7 and 25.9% (19.6-33.3) in wave 8, whilst the proportion aged over 70 was stable.

Conclusions: This demonstrates decreasing COVID-19 related ED workload during successive outbreaks, with an increase in virus-naïve pre-school children and decrease in presentation to case ratio consistent with less severe infections. This suggests that the virus has continued to evolve.