Population Changes in Seroprevalence among a Statewide Sample in the United States

Antibody surveillance provides essential information for public health officials to work with communities to discuss the spread and impact of COVID-19. At the start of the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic in the United States, diagnostic testing was limited with many asymptomatic and thus undetected cases. Irrespective of symptom severity, antibodies develop within two to three weeks after exposure and may persist 6 months or more.; Thus, antibody surveillance is an important tool for tracking trends in past infections across diverse populations. This study includes adults and children ([≥]12 years old) recruited from a statewide sample of past 2014-2020 Survey of the Health of Wisconsin (SHOW) participants. SHOW, an ongoing population-based health examination study including a randomly selected sample of households, partnered with the Wisconsin Department of Health Services and the Wisconsin State Laboratory of Hygiene to conduct longitudinal antibody surveillance using the Abbott Architect SARS-CoV-2 IgG antibody test, which detects antibodies against the nucleocapsid protein. Three WAVES of sample collection were completed in 2020-2021, tracking mid-summer, late fall, and early spring COVID-19 trends prior to vaccine availability. Crude estimates of seroprevalence in the total study population increased ten-fold from 1.4% during WAVE I to 11.5% in WAVE III. Within the statewide probability sample, weighted estimates increased from 1.6% (95% CI:0.6-2.5%), to 6.8% (95% CI:4.3-9.4%) in WAVE II and to 11.4% (95% CI:8.2, 14.6%) in WAVE III. Longitudinal trends in seroprevalence match statewide case counts. Local seroprevalence showed variation by state health region with increasing prevalence among higher income (>200% poverty income ratio), and rural health regions of the state seeing the highest increase in COVID-19 prevalence over time. Significant disparities in prevalence by racial and ethnic groups also exist, with greater than two times seroprevalence among Latino and black participants compared to non-Hispanic whites. This public health and academic partnership provides critical data for the ongoing pandemic response and lays the foundation for future research into longer-term immunity, health impacts and population-level disparities.