Published in PLOS One on 2026-06-15, this study is presented as an attributed evidence briefing. The excerpts below are the original researchers’ words, reproduced under their Creative Commons Attribution licence. Health Signal has selected the abstract and, where needed, opening background paragraphs; the complete methods, results, limitations and references remain in the linked paper.
Original authors: Su D. Yang, Freda Qi, Karen Colwill, Anne-Claude Gingras, Tara S. Beattie, Joshua Kimani, Rupert Kaul
Source: PLOS One • DOI 10.1371/journal.pone.0327692
Read the complete primary study ↗ · Creative Commons Attribution licence
From the researchers
Abstract
While COVID-19 mortality was relatively low in many Sub-Saharan African countries during the first wave of the pandemic, SARS-CoV-2 transmission was extensive. We hypothesized that female sex workers (FSWs) would be at enhanced risk of acquisition of this novel respiratory viral infection, due to intimate contact with multiple sexual partners and solicitation of clients in crowded venues. Here we describe the seroincidence, socio-behavioural associations and clinical outcomes of SARS-CoV-2 infection in Kenyan FSWs early in the pandemic. A longitudinal cohort of 1003 FSWs (257 living with HIV) from Nairobi, Kenya was enrolled in mid-2019, just prior to the pandemic, and plasma was available for SARS-CoV-2 serology from 827 participants at clinical follow up approximately one year later. Socio-behavioural and respiratory symptom data were collected by questionnaire. We examined the association of SARS-CoV-2 infection with socio-behavioural factors. Follow-up was a median of 201 days (range; 92−342 days) after the declaration of the COVID-19 pandemic in Kenya, and 229 (27.7%) participants were SARS-CoV-2 seropositive. Seroprevalence increased steadily with time from pandemic declaration. Infection was not associated with behavioural or demographic parameters but was strongly associated with time since start of the pandemic (p < 0.0001). Respiratory symptoms during the past 6 months were reported by almost two-thirds of participants (510/821; 62.1%), with SARS-CoV-2 infection specifically associated with self-reported difficulty breathing, dizziness, fever, loss of smell, myalgia, rhinorrhea, and odynophagia; approximately half of the cases were completely asymptomatic. HIV status was not associated with differences in SARS-CoV-2 seroincidence or symptoms, and no behavioural or sociodemographic associations of infection were apparent. Pre-pandemic serology demonstrated antibodies recognizing one of SARS-CoV-2 Spike, RBD, or N in 151/994 participants (15.2%), but these were not associated with protection against subsequent SARS-CoV-2 infection. Overall, SARS-CoV-2 seroincidence was high early in the pandemic among Nairobi-based FSWs, with no clear socio-behavioural associations of infection.
Introduction
In late 2019, there were reports of an atypical, pneumonia-like illness beginning to emerge in China, setting the stage for a global health crisis. By January 20th, 2020, the first confirmed case of SARS-CoV-2 infection was reported in the United States, followed by the first reports in Europe just days later, and Africa confirmed its first case on February 14th, 2020. However, the relative burden of COVID-19 disease and mortality during the first wave of the pandemic was low in sub-Saharan Africa (SSA) in comparison to Europe and North America. By 1st February 2021, Europe reported 8.9 times more cases and 8.3 times more deaths than SSA; similarly, North America reported 8.8 and 7.5 times more cases and deaths than SSA, respectively [1]. This reduced burden of SARS-CoV-2 infection and mortality may relate in part to reduced public health surveillance and barriers to nasopharyngeal PCR testing in the region [2,3] since modelling suggests that by the end of 2021 only 1.4% of incident SARS-CoV-2 infections in SSA had been reported [4]. Indeed, retrospective sero-surveys and meta-analyses show that SARS-CoV-2 seroprevalence in African countries was around 40% [5] by October 2020 and upwards of 60% by September 2021 [6]. This indicates that transmission was more widespread than had been appreciated from case-based surveillance, but also suggests that a relatively high proportion of infections in SSA had been asymptomatic – a hypothesis that was subsequently confirmed [6,7].
Reading this evidence
Use the full paper to check the study design, participant selection, comparator and outcome definitions before drawing a practical conclusion. An association does not by itself show cause and effect. A reported performance measure needs its denominator and uncertainty. A finding from a particular facility, sample or time period should retain that scope when it is discussed elsewhere.
This briefing makes the source accessible within the wider research & evidence desk. It does not assess an individual patient or certify a product. When considering relevance to another health system, examine the original authors’ account of context and limitations, then seek local implementation evidence. The related reporting below provides other studies to read alongside this one; it is a topic connection, rather than a claim that their results are directly comparable.
© 2026 Su D. Yang, Freda Qi, Karen Colwill, Anne-Claude Gingras, Tara S. Beattie, Joshua Kimani, Rupert Kaul. Excerpts reproduced under CC BY. Selection, formatting and contextual notes by Health Signal. The researchers are the authors of the source study, not members of Health Signal’s staff.
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