High SARS-CoV-2 incidence and asymptomatic fraction during Delta and Omicron BA.1 waves in The Gambia

• Published in: Nature communications 2024-05, Vol.15 (1), p.3814-3814, Article 3814
• Main Authors: Jarju, Sheikh, Wenlock, Rhys D., Danso, Madikoi, Jobe, Dawda, Jagne, Ya Jankey, Darboe, Alansana, Kumado, Michelle, Jallow, Yusupha, Touray, Mamlie, Ceesay, Ebrima A., Gaye, Hoja, Gaye, Biran, Tunkara, Abdoulie, Kandeh, Sheriff, Gomes, Marie, Sylva, Ellen Lena, Toure, Fatoumata, Hornsby, Hailey, Lindsey, Benjamin B., Nicklin, Martin J., Sayers, Jon R., Sesay, Abdul K., Kucharski, Adam, Hodgson, David, Kampmann, Beate, de Silva, Thushan I.
• Format: Article
• Language: English
• Subjects: 13/1; 631/326/596/4130; 692/308/174; 692/499; Adolescent; Adult; Asymptomatic; Asymptomatic Infections - epidemiology; Child; Child, Preschool; Children; Cohort analysis; COVID-19; COVID-19 - epidemiology; COVID-19 - immunology; COVID-19 - prevention & control; COVID-19 - virology; Female; Gambia - epidemiology; Health risks; Households; Humanities and Social Sciences; Humans; Immunity; Incidence; Infant; Infections; Male; Middle Aged; multidisciplinary; Polymerase chain reaction; Prospective Studies; Risk; SARS-CoV-2 - genetics; SARS-CoV-2 - immunology; Science; Science (multidisciplinary); Serology; Severe acute respiratory syndrome coronavirus 2; Vaccines; Viral diseases; Young Adult
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-48098-3

Little is known about SARS-CoV-2 infection risk in African countries with high levels of infection-driven immunity and low vaccine coverage. We conducted a prospective cohort study of 349 participants from 52 households in The Gambia between March 2021 and June 2022, with routine weekly SARS-CoV-2 RT-PCR and 6-monthly SARS-CoV-2 serology. Attack rates of 45% and 57% were seen during Delta and Omicron BA.1 waves respectively. Eighty-four percent of RT-PCR-positive infections were asymptomatic. Children under 5-years had a lower incidence of infection than 18-49-year-olds. One prior SARS-CoV-2 infection reduced infection risk during the Delta wave only, with immunity from ≥2 prior infections required to reduce the risk of infection with early Omicron lineage viruses. In an African population with high levels of infection-driven immunity and low vaccine coverage, we find high attack rates during SARS-CoV-2 waves, with a high proportion of asymptomatic infections and young children remaining relatively protected from infection. Many low- and middle-income countries, including The Gambia, had low COVID-19 vaccination coverage during the emergence of the Delta and Omicron variants. Here, the authors perform a prospective household cohort study in the Gambia to investigate the dynamics of SARS-Cov-2 infection in this setting.