Abstract
We summarized through systematic review and meta-analysis of observational studies the risk of mortality as well as severe illness of COVID-19 caused by omicron variant relative to delta variant of SARS-CoV-2. A total of twelve studies were included. Our results showed significantly reduced odds of mortality (pooled OR = 0.33; 95% CI: 0.16-0.67) and significantly reduced odds of severe illness (pooled OR = 0.24; 95% CI: 0.21-0.28) in patients infected with the omicron variant of SARS-CoV-2 relative to their counterparts infected with the delta variant. Findings of lower disease severity following infection with the omicron variant of SARS-CoV-2 than the delta variant are encouraging during the ongoing transition from the pandemic phase into the endemic phase of COVID-19.