Background On October, 2020, after the first wave of COVID-19, only 8290 confirmed cases were reported in Kinshasa, Democratic Republic of the Congo, but the real prevalence remains unknown. To guide public health policies, we aimed to describe the prevalence of SARS-CoV-2 IgG antibodies in the general population in Kinshasa. Methods We conducted a cross-sectional, household-based serosurvey between October 22, 2020, and November 8, 2020. Participants were interviewed at home and tested for antibodies against SARS-CoV-2 spike and nucleocapsid proteins in a Luminex based assay. A positive serology was defined as a sample that reacted with both SARS-CoV-2 proteins (100% sensitivity, 99.7% specificity). The overall weighted, age-standardized prevalence was estimated and the infection-to-case ratio was calculated to determine the proportion of undiagnosed SARS-CoV-2 infections. Results A total of 1233 participants from 292 households were included (mean age, 32.4 years; 764 [61.2%] were women). The overall weighted, age-standardized SARS-CoV-2 seroprevalence was 16.6% (95% CI 14.0-19.5). The estimated infection-to-case ratio was 292:1. Prevalence was higher among participants ≥ 40 years than among those ˂18 years (21.2% vs 14.9%, respectively; p˂0.05). It was also higher in participants who reported hospitalization than among those who did not (29.8% vs 16.0%, respectively; p˂0.05). However, differences were not significant in the multivariate model (p=0.1). Conclusion The prevalence of SARS-CoV-2 is much higher than the number of COVID-19 cases reported. These results justify the organization of a sequential series of serosurveys by public health authorities to adapt response measures to the dynamics of the pandemic.

T wo years after the first detected case of in Kinshasa, Democratic Republic of the Congo (DRC), the country experienced 4 subsequent waves of the virus, with peaks in June 2020 and January, June, and December 2021 (1). As observed across countries in Africa, the second wave in DRC was severe compared with the first wave in terms of dis-ease incidence and associated deaths, partly because of lightening of stringent public health countermeasures implemented during the first wave, including international travel restrictions, and the spread of SARS-CoV-2 Beta variant (B.1.351) from southern Africa countries (2,3). By March 6, 2021, a total of 26,468 laboratory-confirmed cases were reported, including 712 virus-related deaths and 132,929 tests performed; Kinshasa accounted for nearly 75% of all reported cases (1).The true burden of COVID-19 in Kinshasa is likely underestimated because PCR testing is conducted mainly on symptomatic persons meeting the case definition, omitting a large portion of persons who become infected with SARS-CoV-2 but are either asymptomatic or paucisymptomatic. Limited testing facilities throughout Africa, combined with the population's underutilization of healthcare services, further widened the gap between the number of actual infections and detected cases (2,4). On the basis of data from a previously conducted household-based survey in Kinshasa after the first wave, we reported an infection-to-case ratio of 292:1 and a prevalence of 16.6% (5). The survey underscored the critical role of serologic surveys as complementary tools to routine testing results for guiding public health interventions.

Background By the end of the third wave of the COVID-19 epidemic (May – October 2021), only 3,130 out of the 57,268 confirmed cases of coronavirus disease 2019 (COVID-19) in the Democratic Republic of Congo (DRC) were reported in Kongo Central. This province, and especially its capital city Matadi has essential trade and exchanges with Kinshasa, the epicenter of the COVID-19 epidemic in DRC. Kinshasa accounted for 60.0% of all cases during the same period. The true burden of COVID-19 in Matadi is likely underestimated. In this study, we aimed to determine the SARS-CoV-2 seroprevalence and associated risk factors after the third wave in Matadi. Methods We conducted a prospective population-based cross-sectional study in October 2021. Consenting participants were interviewed and tested using an ELISA commercial kit. We applied univariable and multivariable analysis to evaluate factors associated with seropositivity and adjusted the seroprevalence for the test kit performance. Results We included 2,210 participants from 489 households. Female participants represented 59.1%. The median age was 27 years (interquartile range 16–45 years). The crude SARS-CoV-2 seroprevalence was 82.3%. Age was identified as the main risk factor as younger age decreased the seropositivity odds. Accounting for clustering at the household level increased the seroprevalence to 83.2%. The seroprevalence increased further to 88.1% (95% CI 86.2–90.1%) after correcting for the laboratory test kit performance. Conclusions The SARS-CoV-2 seroprevalence was very high, contrasting with reported cases. Evidence generated from this population-based survey remains relevant in guiding the local COVID-19 response, especially vaccination strategies.