SARS‐CoV‐2 seroprevalence among blood donors in Uganda: 2019–2022

Abstract

Background The true burden of COVID‐19 in low‐ and middle‐income countries remains poorly characterized, especially in Africa. Even prior to the availability of SARS‐CoV‐2 vaccines, countries in Africa had lower numbers of reported COVID‐19 related hospitalizations and deaths than other regions globally. Methods Ugandan blood donors were evaluated between October 2019 and April 2022 for IgG antibodies to SARS‐CoV‐2 nucleocapsid (N), spike (S), and five variants of the S protein using multiplexed electrochemiluminescence immunoassays (MesoScale Diagnostics, Rockville, MD). Seropositivity for N and S was assigned using manufacturer‐provided cutoffs and trends in seroprevalence were estimated by quarter. Statistically significant associations between N and S antibody seropositivity and donor characteristics in November–December 2021 were assessed by chi‐square tests. Results A total of 5393 blood unit samples from donors were evaluated. N and S seropositivity increased throughout the pandemic to 82.6% in January–April 2022. Among seropositive individuals, N and S antibody levels increased ≥9‐fold over the study period. In November–December 2021, seropositivity to N and S antibody was higher among repeat donors (61.3%) compared with new donors (55.1%; p = .043) and among donors from Kampala (capital city of Uganda) compared with rural regions (p = .007). Seropositivity to S antibody was significantly lower among HIV‐seropositive individuals (58.8% vs. 84.9%; p = .009). Conclusions Despite previously reported low numbers of COVID‐19 cases and related deaths in Uganda, high SARS‐CoV‐2 seroprevalence and increasing antibody levels among blood donors indicated that the country experienced high levels of infection over the course of the pandemic.

High pre‐Delta and early‐Omicron SARS‐CoV‐2 seroprevalence detected in dried blood samples from Kinshasa (D.R. Congo)

“…COVID‐19 seroprevalence reached 90% among the 2022 women cohort. This finding is in agreement with others at a similar time in the continent: serosurveys in Cameroon, Gambia, Uganda and South Africa have reported antibody positivity between 87% and 96% during the Omicron wave 16,17,19,50,54 . Although lower, the 76.5% seroprevalence reported in Kenya by Awandu et al greatly surpasses PCR confirmed cases 25 .…”

“…Within the 2021 blood donor cohort, seroprevalence reached 61%. This finding is slightly lower than others in the country which have reported up to 70% 13,14,48 and similar to surveys in Somalia, 18 Uganda, 19 Nigeria, 22 Burkina Faso 49 or South Africa 50,51 where antibody detection between 56% and 67% by 2021 has been reported. Although much lower seroprevalence has been estimated in studies in the Republic of the Congo (31.8%) 11 and Gabon (13%), 52 both relied on lateral‐flow rapid immunochromatography tests, which could justify the difference.…”

“…by 2022. 57 More likely, the observed increase is related to reexposure to SARS-CoV-2 rather than immunization (particularly after Omicron emergence) similar to that described in Nigeria by Blotch et al 19 Age is a significant risk factor for COVID-19 severity and, in general terms, high antibody titers are found in patients who suffer severe clinical manifestations. 1,58,59 In the 2022 cohort, median levels were significantly higher for patients over 45 years old.…”

“…This finding is in agreement with others at a similar time in the continent: serosurveys in Cameroon, Gambia, Uganda and South Africa have reported antibody positivity between 87% and 96% during the Omicron wave. 16,17,19,50,54 13,18,21,24,50 and upon meta-analysis, 47,53 where seroprevalence was not significantly different by these categories. Some authors have suggested that transmission reached such high levels by…”

“…In contrast, studies in the DRC have found seroprevalences ranging from 48% 12 to 70% 13,14 . A similar phenomenon has occurred in neighboring countries such as Republic of the Congo, 15 Cameroon, 16 Gambia, 17 Somalia, 18 Uganda, 12,14,19 Tanzania, 20 Nigeria 12,21,22 and Kenya, 23–25 where growing evidence indicates pandemic burden has been grossly underestimated.…”