From March 2020 to the emergence of the Omicron variant in late 2021, about 3.8 billion COVID-19 infections and reinfections occurred, with nearly 44% of the world's population infected at least once but with wide regional variations, estimates a statistical analysis of 190 countries and territories published late last week in The Lancet.

Led by Institute for Health Metrics and Evaluation researchers, the COVID-19 Cumulative Infection Collaborators created and refined statistical models of global and location-specific daily and cumulative COVID-19 infections using data from Johns Hopkins University, national databases, and seroprevalence surveys, adjusting for lags in reporting, undercounting of deaths, waning antibody sensitivity, vaccinations, and reinfection by SARS-CoV-2 variants.