Rapidly increasing SARS-CoV-2 seroprevalence and limited clinical disease in three Malian communities: a prospective cohort study

Abstract

Background The extent of SARS-CoV-2 exposure and transmission in Mali and the surrounding region is not well understood, although infection has been confirmed in nearly 14,000 symptomatic individuals and their contacts since the first case in March 2020. We aimed to estimate the cumulative incidence of SARS-CoV-2 in three Malian communities, and understand factors associated with infection. Methods Between 27 July 2020 and 29 January 2021, we collected blood samples along with demographic, social, medical and self-reported symptoms information from residents aged 6 months and older in three study communities at two study visits. SARS-CoV-2 antibodies were measured using a highly specific two-antigen ELISA optimized for use in Mali. We calculated cumulative adjusted seroprevalence for each site and evaluated factors associated with serostatus at each visit by univariate and multivariate analysis. Findings Overall, 94.8% (2533/2672) of participants completed both study visits. A total of 50.3% (1343/2672) of participants were male, and 31.3% (837/2672) were aged <10 years, 27.6% (737/2672) were aged 10-17 years, and 41.1% (1098/2572) were aged >/=18 years. The cumulative SARS-CoV-2 exposure rate was 58.5% (95% CI: 47.5 to 69.4). This varied between sites and was 73.4% (95% CI: 59.2 to 87.5) in the urban community of Sotuba, 53.2% (95% CI: 42.8 to 63.6) in the rural town of Bancoumana, and 37.1% (95% CI: 29.6 to 44.5) in the rural village of Doneguebougou. This equates to an infection rate of approximately 1% of the population every three days in the study communities between visits. Increased age and study site were associated with serostatus at both study visits. There was minimal difference in reported symptoms based on serostatus. Interpretation The true extent of SARS-CoV-2 exposure in Mali is greater than previously reported and now approaches hypothetical herd immunity in urban areas. The epidemiology of the pandemic in the region may be primarily subclinical and within background illness rates. In this setting, ongoing surveillance and augmentation of diagnostics to characterize locally circulating variants will be critical to implement effective mitigation strategies like vaccines. Funding This project was funded by the Intramural Research Program of the National Institute of Allergy and Infectious Diseases, National Institute of Biomedical Imaging and Bioengineering, and National Cancer Institute.

Seroprevalence of Anti-SARS-CoV-2 Antibodies in Senegal: A National Population-Based Cross-Sectional Survey, between October and November 2020

“…Other studies showed the same results in Africa approximately over the same period or at the beginning of 2021, i.e Juba, South-Sudan (22•6% in August-September); or our neighboring country, Mali, 54•7% in Dec-Jan 2021, although these studies concern a part of the population or a targeted population 16,29 . Altogether, this demonstrated an important circulation of SARS-CoV-2 in Senegal and in general in Africa.…”

“…This is corroborated by other studies showing that the rate of infection with the SARS-CoV-2 virus is higher than the rate announced by the surveillance systems. 29,30 This hidden face of the progression of the virus was enhanced by i) a low number of molecular tests carried out and, ii) a lesser proportion of severe cases of the disease as compared to European and American Regions. The severity of COVID-19 disease may be tempered by one of the demographic features of the African population i.e the youth of the Senegalese population (mean age of 19 years), iii) a more robust non-specific immunity gained by multiple and abundant exposures to pathogens that protect against the severe form of COVID-19 and iv) the absence of self-reporting of mild symptoms compatible COVID-19 during the first wave.…”

SARS-CoV-2 seroprevalence and living conditions in Bamako (Mali): a cross-sectional multistage household survey after the first epidemic wave, 2020

“…In Mali, Sagara et al reported in the peri-urban area of Sotuba a crude seroprevalence of 13.1 % (n=587) across samples collected over a 2-month period after the first wave. But the subsequent study conducted in January 2021 in this peri-urban area showed an adjusted seroprevalence rate of 73.4%, after the second COVID-19 wave [6]. This sharp increase in the prevalence rate can be explained by a wave of intense transmission of COVID-19 related to alpha variant in Mali between November 2020 and January 2021 together with the increase of the screening capacity of the health services [4].…”

“…A single survey provides a snapshot of the extent of the virus spread at a given time point, and informs on vulnerable population groups, on the denominators used to calculate infection fatality rate or hospitalization rates [5]. In Mali, a multi-site study including a periurban area of the capital city Bamako demonstrated a sharp increase in seroprevalence between a survey conducted after the first wave of clinical cases (August 2020) and a survey conducted during the decrease of the second wave (January 21), identifying geographical location and age as associated factors [6]. Indeed, Sagara et al reported in the peri-urban area of Sotuba a crude seroprevalence of 13.1 % (n=587) after the first wave.…”

Design of an observational multi-country cohort study to assess immunogenicity of multiple vaccine platforms (InVITE)

“…Subgroup analyses will be based on age, sex, BMI, comorbidities, HIV infection, pregnancy, malaria, or TB and prior infection with SARS-CoV-2 with comparisons within each vaccine regimen. The impact of malaria, dengue, and helminth infections on immune response will be evaluated serologically given that recent data indicate that cross-reactivity has been observed on SARS-CoV-2 serological assays [5][6][7][8][9]. Malaria will be specifically tested for, as there is evidence that indicates it can suppress the immune response to some vaccines [5].…”