SARS-CoV-2 antibody prevalence in Sierra Leone, March 2021: a cross-sectional, nationally representative, age-stratified serosurvey

Abstract

IntroductionAs of 26 March 2021, the Africa Centres for Disease Control and Prevention had reported 4 159 055 cases of COVID-19 and 111 357 deaths among the 55 African Union member states; however, no country has published a nationally representative serosurvey as of October 2021. Such data are vital for understanding the pandemic’s progression on the continent, evaluating containment measures, and policy planning.MethodsWe conducted a cross-sectional, nationally representative, age-stratified serosurvey in Sierra Leone in March 2021 by randomly selecting 120 Enumeration Areas throughout the country and 10 randomly selected households in each of these. One to two persons per selected household were interviewed to collect information on sociodemographics, symptoms suggestive of COVID-19, exposure history to laboratory-confirmed COVID-19 cases, and history of COVID-19 illness. Capillary blood was collected by fingerstick, and blood samples were tested using the Hangzhou Biotest Biotech RightSign COVID-19 IgG/IgM Rapid Test Cassette. Total seroprevalence was estimated after applying sampling weights.ResultsThe overall weighted seroprevalence was 2.6% (95% CI 1.9% to 3.4%). This was 43 times higher than the reported number of cases. Rural seropositivity was 1.8% (95% CI 1.0% to 2.5%), and urban seropositivity was 4.2% (95% CI 2.6% to 5.7%).DiscussionOverall seroprevalence was low compared with countries in Europe and the Americas (suggesting relatively successful containment in Sierra Leone). This has ramifications for the country’s third wave (which started in June 2021), during which the average number of daily reported cases was 87 by the end of the month:this could potentially be on the order of 3700 actual infections per day, calling for stronger containment measures in a country with only 0.2% of people fully vaccinated. It may also reflect significant under-reporting of incidence and mortality across the continent.

Seroprevalence of SARS-CoV-2 antibody among urban Iranian population: findings from the second large population-based cross-sectional study

“…To the best of our knowledge, no similar serosurveys have been done in the same period as our study in Iran (after the third wave) either at the national or regional level, and all available studies pertains to previous waves [ 9 , 28 – 31 ]; hence, we are not able to compare our results with any Iranian studies. The seroprevalence rate estimated in the present study (34.2%) was higher than estimates from the USA, such as Georgia (8.6% [weighted seroprevalence]) [ 32 ], and Cincinnati Ohio (12.9% [unweighted seroprevalence]) [ 33 ], Denmark (4.0% [test-performance adjusted seroprevalence]) [ 34 ], India (24.1% [weighted and test-performance adjusted seroprevalence]) [ 22 ], Sierra Leone (2.6% [weighted seroprevalence]) [ 35 ], and South Africa (27% [test-performance adjusted seroprevalence]) [ 36 ], which could be partly attributed to the fact that the onset of the COVID-19 epidemic in Iran was earlier than the given countries, leading to longer exposure of Iranian population to the virus and a higher risk of the infection. Furthermore, differences in the IPC protocols and their observance, as well as the social and climatic conditions, in each country could be other causes of the discrepancy in the seroprevalence rate.…”

COVID-19 in the 47 countries of the WHO African region: a modelling analysis of past trends and future patterns

“… 18 Looking at these countries, their reported infections at the time of the seroprevalence studies represented a small proportion (one in 50 to one in 200) of their actual burden of COVID-19. 19 , 20 …”

Global SARS-CoV-2 seroprevalence: a systematic review and meta-analysis of standardized population-based studies from Jan 2020-May 2022

“…(5) A new wave of well conducted seroprevalence studies, including many in LMICs, provides robust estimates of seroprevalence in late 2020 and into 2021. (6–8) Synthesizing these studies is crucial to understand the shifting global dynamics and true extent of SARS-CoV-2 infection, humoral immunity, and population susceptibility. While previous global systematic reviews of seroprevalence have been conducted,(9–12) these have included only studies that sampled participants in 2020 and pooled seroprevalence across all time points.…”