*Values are no. (%) participants except as indicated. The study compared SARS-CoV-2 spike antibody data collected during July–October 2021 in the same Dominican Republic provinces from a longitudinal AFI surveillance system embedded in routine healthcare settings (“surveillance”) (4), which included routine blood collection for serologic testing; and a multistage, population-representative household serologic survey (“survey”) (1). Seroprevalence represents the percentage of participants with spike antibody titers above the manufacturer-specified cutoff (≥0.8 U/mL). IQR, interquartile range. †The matched survey dataset was generated through 1:5 nearest-neighbor propensity score matching of survey participants to surveillance participants, using age and number of COVID-19 vaccine doses as matching variables. Because only those variables were included in the propensity model, differences in other characteristics (e.g., province, setting, days since last vaccination) reflect inherent differences between the underlying sampling frames rather than confounding in the matched analysis. ‡Two surveillance participants were missing data for setting.