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. 2022 Jun;27(6):564-573.
doi: 10.1111/tmi.13752. Epub 2022 May 10.

Outcomes of laboratory-confirmed SARS-CoV-2 infection in the Omicron-driven fourth wave compared with previous waves in the Western Cape Province, South Africa

Mary-Ann Davies  1   2   3 , Reshma Kassanjee  2 , Petro Rousseau  4 , Erna Morden  1   3 , Leigh Johnson  2 , Wesley Solomon  4 , Nei-Yuan Hsiao  5   6 , Hannah Hussey  1   3 , Graeme Meintjes  7   8   9 , Masudah Paleker  1   10 , Theuns Jacobs  1 , Peter Raubenheimer  7   8 , Alexa Heekes  1   2 , Pierre Dane  1   2 , Jamy-Lee Bam  1 , Mariette Smith  1   2 , Wolfgang Preiser  6   11 , David Pienaar  12 , Marc Mendelson  7   13 , Jonathan Naude  14 , Neshaad Schrueder  15   16 , Ayanda Mnguni  17 , Sue Le Roux  18   19 , Kathleen Murie  19   20 , Hans Prozesky  15   21 , Hassan Mahomed  10   20 , Liezel Rossouw  19 , Sean Wasserman  7   9   13 , Deborah Maughan  7   8 , Linda Boloko  7   13 , Barry Smith  18   19 , Jantjie Taljaard  15   21 , Greg Symons  7   8 , Ntobeko A B Ntusi  7   8 , Arifa Parker  15   21 , Nicole Wolter  22 , Waasila Jassat  22 , Cheryl Cohen  22   23 , Richard Lessells  24 , Robert J Wilkinson  9   25   26 , Juanita Arendse  19 , Saadiq Kariem  19 , Melvin Moodley  1 , Milani Wolmarans  4 , Keith Cloete  19 , Andrew Boulle  1   2   3 ; Western Cape and South African National Departments of Health in collaboration with the National Institute for Communicable Diseases in South Africa Affiliations
Affiliations

Outcomes of laboratory-confirmed SARS-CoV-2 infection in the Omicron-driven fourth wave compared with previous waves in the Western Cape Province, South Africa

Mary-Ann Davies et al. Trop Med Int Health. 2022 Jun.

Abstract

Objectives: The objective was to compare COVID-19 outcomes in the Omicron-driven fourth wave with prior waves in the Western Cape, assess the contribution of undiagnosed prior infection to differences in outcomes in a context of high seroprevalence due to prior infection and determine whether protection against severe disease conferred by prior infection and/or vaccination was maintained.

Methods: In this cohort study, we included public sector patients aged ≥20 years with a laboratory-confirmed COVID-19 diagnosis between 14 November and 11 December 2021 (wave four) and equivalent prior wave periods. We compared the risk between waves of the following outcomes using Cox regression: death, severe hospitalisation or death and any hospitalisation or death (all ≤14 days after diagnosis) adjusted for age, sex, comorbidities, geography, vaccination and prior infection.

Results: We included 5144 patients from wave four and 11,609 from prior waves. The risk of all outcomes was lower in wave four compared to the Delta-driven wave three (adjusted hazard ratio (aHR) [95% confidence interval (CI)] for death 0.27 [0.19; 0.38]. Risk reduction was lower when adjusting for vaccination and prior diagnosed infection (aHR: 0.41, 95% CI: 0.29; 0.59) and reduced further when accounting for unascertained prior infections (aHR: 0.72). Vaccine protection was maintained in wave four (aHR for outcome of death: 0.24; 95% CI: 0.10; 0.58).

Conclusions: In the Omicron-driven wave, severe COVID-19 outcomes were reduced mostly due to protection conferred by prior infection and/or vaccination, but intrinsically reduced virulence may account for a modest reduction in risk of severe hospitalisation or death compared to the Delta-driven wave.

Keywords: COVID-19; Delta; immunity; omicron; prior infection; sub-Saharan Africa; vaccination.

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Conflict of interest statement

All authors declare that they have no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Daily new cases (7‐day moving average) by days since the start of each wave in (a) the Western Cape Province and (b) Khayelitsha subdistrict, Cape Town, South Africa from 10 March 2020 to 31 December 2021
FIGURE 2
FIGURE 2
Adjusted hazard ratio for associations between (a) vaccination and (b) prior diagnosed infection and different severe COVID‐19 outcomes adjusted for patient characteristics, subdistrict, vaccination and prior diagnosed infection using Cox regression
See this image and copyright information in PMC

Update of

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