Post-Omicron SARS-CoV-2 antibody prevalence in Sierra Leone: A cross-sectional, nationally representative, follow-up serosurvey
Bibliographic record
Abstract
Based on a serosurvey conducted in March 2021, Barrie and colleagues published the first nationally representative SARS-CoV-2 serosurvey in Africa, estimating a SARS-CoV-2 seroprevalence of 2.6% in Sierra Leone, 43 times higher than the reported number of cases at that time. Over the following two years, increasingly transmissible variants-specifically Delta and Omicron-proliferated across the globe, and their impact in Africa is poorly understood. Additional nationally representative seroprevalence data are therefore necessary to understand the pandemic's progression on the continent and for evaluating containment measures and future preparedness. Our follow-up nationally representative survey was conducted in Sierra Leone from February to March 2023. We returned to the 120 Enumeration Areas throughout the country collecting blood samples from one or more individuals per household as well as information on sociodemographic characteristics, history of COVID-19 infection and immunization, and attitudes towards vaccination. The weighted overall seroprevalence (vaccinated and/or SARS-CoV-2 infection) for individuals >19 years of age was 33% (95% CI 29-37). Using the data and distributions from our previous serosurvey, the weighted predicted seroprevalence (any prior SARS-CoV-2 infection) for the general population was 28% (95% CI 15-41). The weighted predicted seroprevalence was ~11 times higher than the pre-Delta/Omicron prevalence. It was also over 300 times higher than the reported number of cases. Despite this, overall seroprevalence was low compared with countries in Europe and the Americas (pointing towards lower transmission in Sierra Leone). In addition, our results suggest the following regarding prevention campaigns claiming to have vaccinated 70% of adults in Sierra Leone as of December 2022: 1) they resulted in limited seroconversion; 2) there was significant waning of immunity; and/or 3) many less individuals were vaccinated than reported. Regardless of the cause, the utility of COVID-19 Vaccine Delivery Partnership (CoVDP) efforts three years into the pandemic is called into question.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".