SARS-CoV-2 Seroprevalence, Cumulative Infections, and Immunity to Symptomatic Infection – A Multistage National Household Survey and Modeling Study, Dominican Republic, June–October 2021

Background: Population-level SARS-CoV-2 immunological protection is poorly understood but can guide vaccination and non-pharmaceutical intervention priorities. Our objective was to characterize cumulative infections and immunological protection in the Dominican RepublicMethods: Household members ≥5 years were enrolled in a three-stage national household cluster serosurvey in the Dominican Republic. We measured pan-immunoglobulin antibodies against the SARS-CoV-2 spike (anti-S) and nucleocapsid glycoproteins, and pseudovirus neutralizing activity against the ancestral and B.1.617.2 (Delta) strains. Seroprevalence and cumulative prior infections were weighted and adjusted for assay performance and seroreversion. Binary classification machine learning methods and pseudovirus neutralizing correlates of protection were used to estimate 50% and 80% protection against symptomatic infection.Findings: Between 30 Jun and 12 Oct 2021 we enrolled 6,683 individuals from 3,832 households. We estimate that 89.5% (79.2–99.8) of the ≥ 5 years population had been immunologically exposed and 77.5% (CI 71.3–83) had been previously infected. Protective immunity sufficient to provide at least 50% protection against symptomatic SARS-CoV-2 infection was estimated in 78.1% (CI 74.3–82) and 66.3% (CI 62.8–70) of the population for the ancestral and Delta strains respectively. Younger (5–14 years, OR 0.47 [CI 0.36–0.61]) and older (≥75-years, 0.40 [CI 0.28–0.56]) age, working outdoors (0.53 [0.39–0.73]), smoking (0.66 [0.52–0.84]), urban setting (1.30 [1.14–1.49]), and three vs no vaccine doses (18.41 [10.69–35.04]) were associated with 50% protection against the ancestral strain.Interpretation: Cumulative infections substantially exceeded prior estimates and overall immunological exposure was high. After controlling for confounders, markedly lower immunological protection was observed to the ancestral and Delta strains across certain subgroups, findings that can guide public health interventions and may be generalizable to other settings and viral strains.Funding Information: This study was funded through a US Centers for Disease Control and Prevention (CDC) U01 Cooperative Agreement and CDC staff supported the design, interpretation, and manuscript editing.Declaration of Interests: Andres Espinosa-Bode and Emily Zielinski Gutiérrez PhD are employees of the US Centers for Disease Control and Prevention. We declare no other competing interests.Ethics Approval Statement: Written consent was obtained for all participants. For children < 18 years old, except emancipated minors, consent was obtained from the legal guardian. Written assent was provided by adolescents 14-17 years old, and verbal assent by children 7-13 years old. The study protocol was approved by the National Council of Bioethics in Health, Santo Domingo (013-2019), the Institutional Review Board of Pedro Henríquez Ureña National University, Santo Domingo, and the Mass General Brigham Human Research Committee, Boston, USA (2019P000094). Study procedures and reporting adhered to STROBE criteria for observational studies.