Analysis of Seroprevalence in Kenya Suggests COVID-19 Virus Exposure More Extensive Than Reported

Kenya Schoolboy

Blood samples from Kenyan donors suggest a broader SARS-CoV-2 exposure than reported through case-based surveillance.

Researchers analyzing blood samples from blood donors across Kenya estimate that by June 2020, when many COVID-19 deaths were expected in the country but hadn’t occurred at such scale, 4.3% of Kenyans had antibodies to the virus. This suggests SARS-CoV-2 exposure has been more extensive than indicated by case-based surveillance in Kenya, the authors say.

Their results will help guide the pandemic response in a region where the economic effects of lockdown — including the way it disrupts routine medical care to women and children — have proven particularly debilitating. Africa accounts for 17% of the global population but by late July 2020, despite evidence of several months of SARS-CoV-2 transmission, it accounted for only 5% of the global COVID-19 cases and 3% of the global COVID-19 deaths.

In Kenya, the first case of SARS-CoV-2 was reported in mid-March 2020, followed quickly by the institution of lockdowns. By end of July, however, national surveillance recorded 20,636 cases and 341 deaths in Kenya — an increase notably slower than the epidemic in parts of China, Europe, and the United States.

Seeking to understand this pattern, Sophie Uyoga and colleagues conducted one of the first field-based seroprevalence surveys in Africa. They analyzed samples collected from more than 3,000 blood transfusion donors from late April to mid-June 2020. Using a highly specific assay, the authors report a crude seroprevalence of 5.6% in this group. Adjusting for the age-sex structure of Kenya, the authors estimate an overall seroprevalence of 4.3%, peaking in younger age groups, which is consistent with other studies.

The authors offer several potential explanations for why Kenya has seen relatively lower cases and deaths even as SARS-CoV-2 exposure appears considerable, including the steep demographic age-pyramid in Kenya, which results in a smaller vulnerable age group. The results of their study, say the authors, support “the impression that disease may be attenuated in Africa.”

Reference: “Seroprevalence of anti–SARS-CoV-2 IgG antibodies in Kenyan blood donors” by Sophie Uyoga, Ifedayo M. O. Adetifa, Henry K. Karanja, James Nyagwange, James Tuju, Perpetual Wanjiku, Rashid Aman, Mercy Mwangangi, Patrick Amoth, Kadondi Kasera, Wangari Ng’ang’a, Charles Rombo, Christine Yegon, Khamisi Kithi, Elizabeth Odhiambo, Thomas Rotich, Irene Orgut, Sammy Kihara, Mark Otiende, Christian Bottomley, Zonia N. Mupe, Eunice W. Kagucia, Katherine E. Gallagher, Anthony Etyang, Shirine Voller, John N. Gitonga, Daisy Mugo, Charles N. Agoti, Edward Otieno, Leonard Ndwiga, Teresa Lambe, Daniel Wright, Edwine Barasa, Benjamin Tsofa, Philip Bejon, Lynette I. Ochola-Oyier, Ambrose Agweyu, J. Anthony G. Scott and George M. Warimwe, 11 November 2020, Science.
DOI: 10.1126/science.abe1916

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