Survey Design and Population
We designed a cross-sectional, age-stratified SARS-CoV-2 seroepidemiological survey in community-based sites across 10 regional capitals of Cameroon, in line with the World Health Organization (WHO) UNITY studies framework.13, This survey took place from October to December 2020 at 30 purposively selected community-based sites (three in each regional capital), including marketplaces, bus stops, and busy commercial intersections. High traffic venues were chosen because they most likely had a broad representation of age groups, sexes, and socioeconomic statuses. The sites were selected in conjunction with local stakeholders [Cameroon Ministry of Health, U.S. Centers for Disease Control and Prevention (CDC) in Cameroon]. For a more representative sample of the regional population, we set regional quotas for three broad age groups: 5-19 years, 20-49 years, and 50+ years (Appendix Table 1). The quotas were proportional to the regional population based on census data (2020) for each of these age groups.14
Children < 5 years were excluded due to the difficulty in obtaining blood from young children, especially in such public settings. At each site, survey staff used banners and other promotional materials and loudspeakers to announce the survey and attract attention to the on-site survey tent. If participants were traveling in groups, only one adult and one child (5 years and above) per household were eligible to participate based on self-reported relationships. Data were collected at each site for approximately three weeks, until quotas were met.
Prior to participation in the survey, written informed consent was obtained from adults (aged ≥21 years as per Cameroon regulations) and emancipated minors and from parents for participants aged ≤20 years. Written informed assent was also obtained from participants aged 10-20 years. The survey was approved by the Cameroon National Research Ethics Committee and Columbia University reviewed and designated it as public health surveillance. The study was reviewed in accordance with the U.S. CDC human research protection procedures and was determined as research. However the CDC investigators did not interact with any individuals or have access to identifiable data or specimens for research purposes.