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SA cohort study shows reduced chance of death or severe illness with Omicron

Unvaccinated people infected with the Omicron variant of coronavirus may be less prone to severe illness and requiring hospital care or dying than was the case with previous variants, a South African study showed last Wednesday (12 January).

The study, led by Western Cape universities, the Health Department and the National Institute of Communicable Diseases (NICD), awas posted on medRxiv. It compared about 11,600 patients from the first three COVID-19 waves with about 5,100 from the Omicron-driven wave that began in November.

Omicron globally has tended to cause less severe disease, and proportionally fewer hospital admissions and deaths, than previous variants.

Scientists are trying to determine the extent to which this is because of higher immunity rates engendered by vaccination or past illness, or Omicron is intrinsically less nasty.

The study concluded that about a quarter of the reduced risk of severe disease with Omicron was attributable to characteristics of the virus itself.

“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 an approximately 25% reduced risk of severe hospitalisation or death compared with Delta,” the study said.

Study details

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

MaryAnn Davies, Reshma Kassanjee, Petro Rosseau, Erna Morden, Leigh Johnson, Wesley Solomon, NeiYuan Hsiao, Hannah Hussey, Graeme Meintjes, Masudah Paeker, Theuns Jacobs, Peter Raubenheimer, Alexa Heekes, Pierre Dane, Jamy-Lee Bam, Mariette Smith, Wolfgang Preiser, David Pienaar, Marc Mendelson, Jonathan Naude, Neshaad Schrueder, Ayanda Mnguni, Sue Le Roux, Katie Murie, Hans Prozesky, Hassan Mahomed, Liezel Rossouw, Sean Wasserman, Deborah Maughan, Linda Boloko, Barry Smith, Jantjie Taljaard, Greg Symons, Ntobeko Ntusi, Arifa Parker, Nicole Wolter, Waasila Jassat, Cheryl Cohen, Richard Lessells, RobertJ Wilkinson, Juanita Arendse, Saadiq Kariem, Melvin Moodley, Krish Vallabhjee, Milani Wolmarans, Keith Cloete, Andrew Boulle.

Posted on medRxiv on 12 January 2022

Abstract

Objectives
We aimed to compare COVID-19 outcomes in the Omicron-driven fourth wave with prior waves in the Western Cape, the contribution of undiagnosed prior infection to differences in outcomes in a context of high seroprevalence due to prior infection, and 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-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 hospitalization or death (all ≤14 days after diagnosis) adjusted for age, sex, comorbidities, geography, vaccination and prior infection.

Results
We included 5,144 patients from wave four and 11,609 from prior waves. 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 an approximately 25% reduced risk of severe hospitalisation or death compared to Delta.

 

medRxiv article – Outcomes of laboratory-confirmed SARS-CoV-2 infection in the Omicron-driven fourth wave compared with previous waves in the Western Cape Province (Open access)

 

See more from MedicalBrief archives:

 

Omicron has higher asymptomatic carriage rate – Ubuntu study\

 

Omicron variant: Clinical severity and hospitalisation profile in South Africa

 

So far, milder disease seen with Omicron, with shorter hospital stays — SA hospitals analysis

 

 

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