EClinicalMedicine (Feb 2023)

Omicron B.1.1.529 variant infections associated with severe disease are uncommon in a COVID-19 under-vaccinated, high SARS-CoV-2 seroprevalence population in MalawiResearch in context

  • Upendo L. Mseka,
  • Jonathan Mandolo,
  • Kenneth Nyoni,
  • Oscar Divala,
  • Dzinkambani Kambalame,
  • Daniel Mapemba,
  • Moses Kamzati,
  • Innocent Chibwe,
  • Marc Y.R. Henrion,
  • Kingsley Manda,
  • Deus Thindwa,
  • Memory Mvula,
  • Bright Odala,
  • Raphael Kamng'ona,
  • Nelson Dzinza,
  • Khuzwayo C. Jere,
  • Nicholas Feasey,
  • Antonia Ho,
  • Abena S. Amoah,
  • Melita Gordon,
  • Todd D. Swarthout,
  • Amelia Crampin,
  • Robert S. Heyderman,
  • Matthew Kagoli,
  • Evelyn Chitsa-Banda,
  • Collins Mitambo,
  • John Phuka,
  • Benson Chilima,
  • Watipaso Kasambara,
  • Kondwani C. Jambo,
  • Annie Chauma-Mwale

Journal volume & issue
Vol. 56
p. 101800

Abstract

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Summary: Background: The B.1.1.529 (Omicron) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in the fourth COVID-19 pandemic wave across the southern African region, including Malawi. The seroprevalence of SARS-CoV-2 antibodies and their association with epidemiological trends of hospitalisations and deaths are needed to aid locally relevant public health policy decisions. Methods: We conducted a population-based serosurvey from December 27, 2021 to January 17, 2022, in 7 districts across Malawi to determine the seroprevalence of SARS-CoV-2 antibodies. Serum samples were tested for antibodies against SARS-CoV-2 receptor binding domain using WANTAI SARS-CoV-2 Receptor Binding Domain total antibody commercial enzyme-linked immunosorbent assay (ELISA). We also evaluated COVID-19 epidemiologic trends in Malawi, including cases, hospitalisations and deaths from April 1, 2021 through April 30, 2022, collected using the routine national COVID-19 reporting system. A multivariable logistic regression model was developed to investigate the factors associated with SARS-CoV-2 seropositivity. Findings: Serum samples were analysed from 4619 participants (57% female; 60% aged 18–50 years), of whom 878/3794 (23%) of vaccine eligible adults had received a single dose of any COVID-19 vaccine. The overall assay-adjusted seroprevalence was 83.7% (95% confidence interval (CI), 79.3%–93.4%). Seroprevalence was lowest among children <13 years of age (66%) and highest among adults 18–50 years of age (82%). Seroprevalence was higher among vaccinated compared to unvaccinated participants (1 dose, 94% vs. 77%, adjusted odds ratio 4.89 [95% CI, 3.43–7.22]; 2 doses, 97% vs. 77%, aOR 6.62 [95% CI, 4.14–11.3]). Urban residents were more likely to be seropositive than those from rural settings (91% vs. 78%, aOR 2.76 [95% CI, 2.16–3.55]). There was at least a two-fold reduction in the proportion of hospitalisations and deaths among the reported cases in the fourth wave compared to the third wave (hospitalisations, 10.7% (95% CI, 10.2–11.3) vs. 4.86% (95% CI, 4.52–5.23), p < 0.0001; deaths, 3.48% (95% CI, 3.18–3.81) vs. 1.15% (95% CI, 1.00–1.34), p < 0.0001). Interpretation: We report reduction in proportion of hospitalisations and deaths from SARS-CoV-2 infections during the Omicron variant dominated wave in Malawi, in the context of high SARS-CoV-2 seroprevalence and low COVID-19 vaccination coverage. These findings suggest that COVID-19 vaccination policy in high seroprevalence settings may need to be amended from mass campaigns to targeted vaccination of reported at-risk populations. Funding: Supported by the Bill and Melinda Gates Foundation (INV-039481).

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