The world is experiencing a huge wave of infection with the omicron variant of SARS-CoV-2. Estimates based on Institute for Health Metrics and Evaluation (IHME) models1 suggest that on around Jan 17, 2022 there were 125 million omicron infections a day in the world, which is more than ten times the peak of the delta wave in April, 2021.1 The omicron wave is inexorably reaching every continent with only a few countries in eastern Europe, North Africa, southeast Asia, and Oceania yet to start their wave of this SARS-CoV-2 variant. The unprecedented level of infection suggests that more than 50% of the world will have been infected with omicron between the end of November, 2021 and the end of March, 2022.1 Although IHME models suggest that global daily SARS-CoV-2 infections have increased by more than 30 times from the end of November, 2021 to Jan 17, 2022, reported COVID-19 cases in this period have only increased by six times.1, 2 Because the proportion of cases that are asymptomatic or mild has increased compared with previous SARS-CoV-2 variants,3, 4 the global infection-detection rate has declined globally from 20% to 5%.
Understanding the burden of omicron depends crucially on the proportion of asymptomatic infections. A systematic review based on previous SARS-CoV-2 variants suggested that 40% of infections were asymptomatic. Evidence suggests that the proportion of asymptomatic infections is much higher for omicron, perhaps as high as 80–90%. Garrett and colleagues found that among 230 individuals in South Africa enrolling in a clinical trial, 71 (31%) were PCR positive for SARS-CoV-2 and had the omicron variant and no symptoms.Assuming this prevalence of infection was representative of the population, the implied incidence compared to detected cases suggests that more than 90% of infections were asymptomatic in South Africa.
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