The Sobering Story of SARS-CoV-2 Seroprevalence: What You May Have Heard About Herd Immunity .

Asymptomatic infection remains a major challenge in COVID-19 control, with CDC estimates suggesting that roughly four in ten infected individuals never develop symptoms but can still spread the virus. Because these cases often go undetected, seroprevalence surveys—tests that detect antibodies to SARS-CoV-2—have become essential for understanding true infection levels. Early studies from countries such as Italy, Spain, the U.S., Brazil, and Switzerland consistently show low antibody prevalence, typically well under 10% and peaking around 23% in one Italian region. These numbers fall far short of the estimated 43% immunity threshold needed to slow transmission, reinforcing that natural infection won’t bring populations close to herd immunity. The evidence points clearly toward vaccination—not passive spread—as the only realistic and ethical path to achieving community-level protection.