As of December 28, 2021, approximately 27% of the US population was unvaccinated against SARS-CoV-2,1 yet the prevalence of natural immunity remains unknown. Blood donor studies may have selection bias and lack clinical information.2 Previous COVID-19 infection is a possible surrogate for natural immunity, but 1 study suggested that 36% of COVID-recovered individuals are serologic nonresponders.3 Even among individuals who develop antibodies, durability of this response beyond 6 months remains unknown. We characterized natural immunity and long-term durability among unvaccinated individuals using anti–spike antibodies, the first line of defense against SARS-CoV-2. Methods
Healthy adults who reported no SARS-CoV-2 vaccination were recruited via 1 public Twitter post and 1 public Facebook advertisement between September 11, 2021, and October 8, 2021. Participants completed an online questionnaire about demographics, COVID-19 status, and mask use. Using weighted random sampling (relative weights based on the estimated unvaccinated US population by age, race and ethnicity, and education1), we created 3 equally sized sample groups among those who reported a test-confirmed COVID-19 infection (“COVID-confirmed”), believed they had COVID-19 but were never tested (“COVID-unconfirmed”), and did not believe they ever had COVID-19 and never tested positive (“no-COVID”). These groups were invited to undergo antibody testing at LabCorp facilities nationwide…..