Severity and outcomes of Omicron variant of SARS-CoV-2 compared to Delta variant and severity of Omicron sublineages: a systematic review and metanalysis - Lisa Askie; Maria D Van Kerkhove; Janet Diaz; Olivier Le Polain de Waroux; Nkengafac Villyen Motaze; Pryanka Relan; Bharath Kumar Tirupakuzhi Vijayaraghavan; Kavita Kothari (BMJ Global Health, 2023)