Mild and moderate COVID-19 during Alpha, Delta and Omikron pandemic waves in urban Maputo, Mozambique, December 2020-March 2022: a population-based surveillance study

In sub-Saharan Africa, reported COVID-19 numbers have been lower than anticipated, even when considering populations' younger age. The extent to which risk factors, established in industrialised countries, impact the risk of infection and of disease in populations in sub-Saharan Africa, remains unclear. We estimated the incidence of mild and moderate COVID-19 in urban Mozambique and analysed factors associated with infection and disease in a population-based surveillance study. During December 2020-March 2022, households of a population cohort in Polana Canico, Maputo, Mozambique, were contacted biweekly. Residents reporting any respiratory sign, anosmia, or ageusia, were asked to self-administer a nasal swab, for SARS-CoV-2 PCR testing. Of a subset of 1400 participants, dried blood spots were repeatedly collected three-monthly from finger pricks at home. Antibodies against SARS-CoV-2 spike glycoprotein and nucleocapsid protein were detected using an in-house developed multiplex antibody assay. We estimated the incidence of respiratory illness and COVID-19, and SARS-CoV-2 seroprevalence. We used Cox regression models, adjusting for age and sex, to identify factors associated with first symptomatic COVID-19 and with SARS-CoV-2 sero-conversion in the first six months. During 11925 household visits in 1561 households, covering 6049 participants (median 21 years, 54.8% female, 7.3% disclosed HIV positive), 1895.9 person-years were followed up. Per 1000 person-years, 364.5 (95%CI 352.8-376.1) respiratory illness episodes of which 72.2 (95%CI 60.6-83.9) COVID-19 confirmed, were reported. Of 1412 participants, 2185 blood samples were tested (median 30.6 years, 55.2% female). Sero-prevalence rose from 4.8% (95%CI 1.1-8.6%) in December 2020 to 34.7% (95%CI 20.2-49.3%) in June 2021, when 3.0% were vaccinated. Increasing age (strong gradient in hazard ratio, HR, up to 15.70 in >=70 year olds, 95%CI 3.74-65.97), leukaemia, chronic lung disease, hypertension, and overweight increased risk of COVID-19. We found no increased risk of COVID-19 in people with HIV or tuberculosis. Risk of COVID-19 was lower among residents in the lowest socio-economic quintile (HR 0.16, 95%CI 0.04-0.64), with no or limited handwashing facilities, and who shared bedrooms (HR 0.42, 95%CI 0.25-0.72). Older age also increased the risk of SARS-CoV-2 seroconversion (HR 1.57 in 60-69 year olds, 95%CI 1.03-2.39). We found no associations between SARS-CoV-2 infection risk and socio-economic, behavioural factors and comorbidities. Active surveillance in an urban population cohort confirmed frequent COVID-19 underreporting, yet indicated that the large majority of cases were mild and non-febrile. In contrast to industrialised countries, deprivation did not increase the risk of infection nor disease. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by a European & Developing Countries Clinical Trials Partnership (EDCTP) project (RIA2020EF-3031). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The National health bio-ethics committee of Mozambique (517/CNBS/2020) and the Antwerp University Hospital ethics committee (B3002020000123) gave ethical approval for this work I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Pseudonymized data supporting the findings of this study/publication are retained at the Institute of Tropical Medicine, Antwerp and can be made available after approval of a motivated and written request to ITMresearchdataaccess@itg.be. Study protocol, data dictionaries, scripts for conducting the analysis, and anonymized data, without geo-located or other data that could allow identification, are available on https://github.com/ingelbeen/africover-git