Christopher J L Murray writes:

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) models 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. 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. 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. Because the proportion of cases that are asymptomatic or mild has increased compared with previous SARS-CoV-2 variants, 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. The UK Office for National Statistics (ONS) infection survey estimated a point prevalence of PCR positive SARS-CoV-2 infection of 6·85% for England on Jan 6, 2022. Hospital admission prescreening of individuals without COVID-19 symptoms in the University of Washington Medical Center in Seattle, WA, USA, did not exceed 2% throughout the COVID-19 pandemic but exceeded 10% in the week of Jan 10, 2022 (Murray CJL, unpublished). In addition to the much larger proportion of asymptomatic infections, in the USA the ratio of COVID-19 hospitalisations to detected cases hospitalised has declined by about 50% in most states compared with previous peaks. The proportion of COVID-19 patients in hospital who require intubation or are dying has declined by as much as 80–90% in Canada and South Africa. [Continue reading…]