In 2020, The Gambia had a population of ≈2.42 million. The median age is 17.8 years, and ≈41.9% of the population are 20–64 years of age. About 95% of the population is Muslim. The illiteracy rate is high across the country. Around 59% of the population live in urban and peri-urban settings, mainly along the coast (Figure 1).

The climate is typical of the sub-Sahel region, including a long dry season during November–May and a short rainy season during June–October. Maximum temperature is high throughout the year, 30°C–34°C, and lowest during the rainy season; minimum temperatures range from 22°C–24°C during the rainy season to 16°C−20°C during the dry season (14). Humidity can be >80% during the rainy months (15).

The government of The Gambia is the main health provider, and healthcare delivery has 3 tiers, based on the primary healthcare strategy in which most healthcare delivery occurs at local health posts. The Gambia has 4 tertiary hospitals, 38 health centers at the secondary level, and 492 health posts at the primary level. The system is complemented by 34 private and nongovernmental organization clinics.

Shortly after the first COVID-19 case was detected in The Gambia on March 19, 2020, the country closed its international land, sea, and air borders. On March 27, the country declared a state of emergency, which included closing schools, nonessential shops, places of worship, and many workplaces. Initial SARS-CoV-2 testing by PCR was focused on identifying imported cases and tracing and isolating case contacts, especially among travelers from Senegal. The Ministry of Health, supported by several international organizations, set up a hotline for the public, which persons, including those with suspected cases, could call to ask for advice or request the surveillance team to perform the SARS-CoV-2 test either at health facilities or at home.

As the epidemic progressed, the Ministry of Health established testing facilities at strategic locations in the most densely populated parts of the country, mainly the western urban areas. Persons were encouraged to go for testing if they were symptomatic or after contact with a confirmed COVID-19 case. Demand for testing services was not high, and attempts to raise awareness were unsuccessful. All identified cases were isolated in designated facilities regardless of symptoms until considered noninfectious as per World Health Organization (WHO) guidelines (16). Ministry of Health staff traced and quarantined contacts for 10 days in hotels during the early part of the outbreak, April–July 2020, after which persons were permitted to self-isolate for 10 days at home.

MRCG is a biomedical research institution that also provides outpatient and inpatient clinical care to the local population through its clinical services department (CSD). As of August 2020, MRCG had 1,336 employees. Staff were distributed as follows: 845 were along the coast, mainly in Fajara; 158 were in Keneba; 116 were in the Central River Division, mainly in Farafenni; and 217 were in the Upper River Division, mainly Basse (Figure 1). MRCG staff work in different environments, including 715 (53.5%) field-based staff, such as drivers, community workers, nurses, and research clinicians; 334 (25.0%) office-based staff, including those in administrative, operations, data-management, and statistics positions; and 177 (13.2%) laboratory-based staff. Only 110 (8.2%) MRCG staff provide healthcare to the general population at the CSD.

CSD is 1 of 2 hospital facilities in The Gambia able to care for severe COVID-19 patients. CSD dedicated 42 beds for COVID-19 patients, including MRCG staff and the general population. From the start of the epidemic, all staff were trained to wear appropriate personal protective equipment (PPE) according to international guidelines (17).

MRCG staff underwent a clinician-administered risk assessment in the early phases of the epidemic. Staff deemed to be at high risk for severe disease were advised to work from home and were excluded from high-risk clinical areas.

In July 2020, MRCG established enhanced passive case detection by testing all staff exhibiting COVID-19 symptoms, such as cough, fever, headache, sore throat, nasal congestion, body pain, or other influenza-like symptoms. Families and contacts of symptomatic staff also were tested, as were staff known to have been exposed to confirmed cases. In addition, CSD staff were offered active weekly PCR-based testing, regardless of symptoms. MRCG set up a hotline manned by doctors from whom staff could receive answers to questions or concerns and get information on how to access services. Case contacts were called to confirm exposure and then tested 3–5 days after the last exposure. Regardless of negative test results, all exposed staff were quarantined for 14 days; SARS-CoV-2–positive staff isolated in their homes for 14 days, or at the MRCG site if at-home isolation was not possible, in line with WHO recommendations (18).

Samples were collected via nasopharyngeal swab, oropharyngeal swab, or both by using FLOQSwabs (COPAN Diagnostics, https://www.copanusa.com). Samples were placed in single tubes containing universal transport medium (COPAN Diagnostics) and delivered to the laboratory within 24 hours. Sampling methods were comparable across cohorts with similar operational procedures and training.

MRCG laboratories collaborated with national public health laboratories to support national testing throughout the country during the epidemic. MRCG and these laboratories used the same laboratory methods and assays. Because the outbreak was expected to spread to the West Africa subregion, MRCG staff attended an Africa Centres for Disease Control and Prevention (https://africacdc.org) regional training workshop on diagnosing COVID-19, which was held in February 2020 in Dakar, Senegal. Thereafter, The Gambia established laboratory protocols for processing and testing suspected SARS-CoV-2–infected samples according to WHO guidelines (19,20). The same procedures and assays were transferred to the laboratory.

The standard test for COVID-19 diagnosis in The Gambia is real-time reverse transcription PCR (RT-PCR) of SARS-CoV-2–specific viral gene sequences. In the early stages of the outbreak, RT-PCR diagnosis was made by using the Berlin Charité Laboratory protocol (21), which targets the RNA-dependent RNA polymerase and envelope protein gene. Subsequent tests kits, primarily the Da An Gene Nucleic Acid Extraction Kit (Da An Gene Co., Ltd., of Sun Yat-sen University, https://en.daangene.com) and Novel Coronavirus (2019-nCoV) Nucleic Acid Diagnostic Kit (Sansure Biotech, Inc., http://eng.sansure.com.cn) were donated to the national public health libraries; both tests target the open reading frame 1ab and the nucleocapsid gene coding regions.

Sample inactivation and downstream RNA extraction were done by using commercially available kits according to the manufacturers’ protocols. Initial extractions were performed manually by using the QIAamp Viral RNA Mini Kit (QIAGEN, https://www.qiagen.com) or the IndiSpin Pathogen Kit (INDICAL BIOSCIENCE, https://www.indical.com). When donations to the public health system became available, kits from the Da An Gene Co., Ltd., of Sun Yat-sen University and Sansure Biotech, Inc., were included. As the outbreak progressed and daily sample numbers increased, automated RNA extraction system on the QIAcube HT (QIAGEN) was implemented. In all cases, 200 µL of universal transport medium sample was processed, and the RNA eluted in 50–80 µL, depending on the extraction kit. RT-PCR analysis was conducted with 5 µL of extracted RNA in 25 µL of reaction mix containing reaction buffer, one-step reverse transcription enzyme, either the Takara One Step PrimeScript III RT-PCR Kit (TaKaRa Bio, Inc., http://www.takara-bio.com) or SuperScript III Platinum One-Step qRT-PCR Kit (Invitrogen, https://www.thermofisher.com), and the primer and probe mix.

Samples were defined as positive if amplification of any viral gene occurred after 40 cycles and with all the controls amplifying as appropriate. We defined a COVID-19 case as any person with a SARS-CoV-2–positive RT-PCR from an nasopharyngeal or oropharyngeal swab sample, regardless of symptomatology.

We calculated rates of risk for COVID-19 per 1,000 persons among the population of The Gambia. For MRCG, we stratified rates by occupational clinical exposure for staff working at the CSD versus non-CSD staff. In addition to occupational clinical exposure, surveillance for CSD staff was more intense due to routine testing, regardless of symptoms or known exposure.

The Ministry of Health generated daily national data for The Gambia (22). We extracted compiled data from the publicly available Johns Hopkins University COVID-19 database (23). The Gambian Government/MRCG Joint Ethics committee approved the study (reference no. L2020.E37).

From the start of the epidemic through September 30, 2020, a total of 17,885 samples were tested in The Gambia; 20.1% (3,590) were SARS-CoV-2–positive. The positivity rate was lower before July (1.6%; 40/3,095 samples tested) and higher during July–September (23.7%; 3,499/14,790 samples tested) (19,20). The number of samples collected and the positivity rate were the highest during August–September 2020, during which time the number of daily swabs collected varied from 28 to 524/day (median 184/day) (Figure 2). Positivity rate also varied substantially, from <5% to >50%. Approximately 67% of confirmed cases were detected in August; overall, 60% of confirmed cases were among persons <40 years of age (20).

During July 1–September 30, a total of 937 samples were collected from the MRCG cohort; 191 (20.4%) were SARS-CoV-2–positive. Most (60%) confirmed cases were detected in August. The median age among MRCG staff with SARS-CoV-2–positive samples was 36 years.

By the end of September 2020, the cumulative rate of infection among the population of The Gambia ≈1.5/1,000 persons (Figure 3, panel A). During the same period, 115 COVID-19 deaths were recorded across the country.

Among MRCG staff, stratified analysis showed that infection rates among CSD staff were 2.6 times higher than among non-CSD staff, whom we considered representative of the infection risk among the general population (Figure 3, panel B). By the end of September, the cumulative risk for infection among non-CSD MRCG staff was ≈124/1,000 persons (Figure 3, panel B). All 191 confirmed cases among MRCG staff were either asymptomatic or mildly symptomatic; no cases met WHO criteria for moderate or severe pneumonia and no deaths occurred in this cohort.