Abstract
Background: The extent of SARS-CoV-2 circulation in many African countries remains unclear, underscoring the need for antibody sero-surveys to accurately assess the cumulative attack rate. Methods: We conducted a community-based, cross-sectional sero-survey in Cité Verte, a densely-populated district of Yaoundé, Cameroon, from October 14 to November 26, 2020. Households were randomly selected from a set of all putative residential buildings in the district, and residents between five and 80 years of age were surveyed. The Abbott Panbio SARS-CoV-2 nucleocapsid IgM/IgG rapid antibody test was administered, along with a questionnaire on disease symptoms and health-seeking behavior. Final seroprevalence estimates were adjusted for test accuracy and re-weighted to the city’s age-sex distribution. Random-intercept logistic regression was used to identify risk factors for anti-SARS-CoV-2 IgG seropositivity. Findings: Of 255 households randomly selected, 180 (70·6%) agreed to participate, yielding a sample of 971 participants. The adjusted seroprevalence of SARS-CoV-2 IgG antibodies was 29·2% (95%CI 24·3–34·1). Out of the 302 IgG seropositive individuals, the majority (64·2% [58·7–69·4]) did not report any symptoms over the pandemic period, and most (91·1% [87·3–93·8]) did not consult medical care. Significantly greater odds of IgG seropositivity was found for men (OR: 1·61 [95%CI 1·2–2·2]), residents of households with six or more residents (OR: 1·6 [1·1–2·4]; reference: households with three to five residents) and individuals with a BMI above 30 kg/m² (OR: 1·84 [1·1–3·0]; reference: 18·5–24.9 kg/m²).  Interpretation: By November 2020, the cumulative attack rate of COVID-19 was high in this Cameroonian city, about 323 times greater than the 0.09% nationwide attack rate implied by PCR and antigen- confirmed case counts at the time. The predominantly asymptomatic nature of cases may explain the low COVID-19-related healthcare consultation. Despite the high seroprevalence, most of the population has not been infected with SARS-CoV-2, underlining the importance of continued measures to control viral spread and of quick vaccine deployment to protect the vulnerable. Funding: The UHC Program and Bilateral Health Project in Cameroon of the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, the P4H Health Financing Network, and the Canton of Geneva. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The study protocol obtained the ethical clearance (N°2020/09/1292/CE/CNERSH/SP) and the administrative authorization of the Ministry of Health of Cameroon (N°D30- 845/L/MINSANTE/SG/DROS).
Highlights
The extent of SARS-CoV-2 circulation in many African countries remains unclear, underlining the need for antibody sero-surveys to assess the cumulative attack rate
Multiple hypotheses have been advanced to explain the seemingly mild trajectory of the COVID-19 epidemic in Africa: researchers have pointed to warm climate conditions across much of the continent, timely and effective preventive measures put in place by governments, the young and predominantly rural population, and cross-reactive immunity from other infections as potential mitigating factors[2,4]
It is notable that by this date, only 24,002 cases had been officially reported in the entire country, which has a population of 26.55 million people[15]
Summary
The extent of SARS-CoV-2 circulation in many African countries remains unclear, underlining the need for antibody sero-surveys to assess the cumulative attack rate. Among the 971 participants, the test-adjusted seroprevalence of anti-SARS-CoV-2 IgG antibodies was 29·2% (95% CI 24·3–34·1) This is about 322 times greater than the 0.09% nationwide attack rate implied by COVID-19 case counts at the time. The true scale of the epidemic in many African countries is still unclear, as the PCR and antigen-confirmed case counts that are commonly relied upon may understate viral spread[2,5]. In this context, the use of serological antibody tests to detect past exposure to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is valuable. They are valuable for accurately assessing the cumulative attack rate—the proportion of the population that has ever been infected with SARS-CoV-2
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