Past SARS-CoV-2 Infection Protection Against Reinfection Systematic Review and Meta-Analysis Estimates

Researchers at IHME systematically reviewed, identified, and extracted data from scientific literature studies that estimated the reduction in risk of COVID-19 among individuals with a past SARS-CoV-2 infection in comparison to those without a previous infection. The outcomes assessed were reinfection, symptomatic reinfection, and severe reinfection (hospitalization or death). Extracted SARS-CoV-2 lineages were ancestral, mixed (two different specified variants – e.g., ancestral and Alpha), Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2), and Omicron (BA.1) and its sub-lineages (BA.2, BA.4/BA.5). A total of 65 studies from 19 different countries were identified. The researchers also produced a meta-analysis of the effectiveness of past infection by outcome (infection, symptomatic disease, and severe disease), variant, and time since infection.