Asymptomatic SARS-CoV-2 infections tend to occur less frequently in developed nations

Abstract

Unlike severe infections, asymptomatic infections occur independently of healthcare access and reflect the natural immunity to SARS-CoV-2. What determines their prevalence,ψ, and its variation across nations is unknown. We conducted a systematic review of serosurveys performed on samples representative of national populations before vaccination and the emergence of variants. The studies that met our selection criteria together sampled 4,58,489 individuals and yielded estimates ofψin 33 nations. Using random-effects modeling, we found the pooled globalψto be 45.3% (95% CI: 33.6%-57.5%).ψvaried widely across nations (range: 6%-96%;I2=99.7%), highlighting the enormous underlying variation in the natural immunity to SARS-CoV-2. Performing meta-regression with national-level metrics, we found that the human development index (HDI) was negatively correlated withψ(p=10−13;R2=65.5%). More developed nations thus experienced less frequent asymptomatic infections on average. These findings have implications for unraveling the origins of asymptomatic infections and for future pandemic preparedness.