Omicron vs Delta | Vaccine efficacy reduced from 80% to 33%

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While the Omicron variant is highly transmissible, its severity of illness is significantly reduced compared with the Delta variant. Photo: Getty Images
While the Omicron variant is highly transmissible, its severity of illness is significantly reduced compared with the Delta variant. Photo: Getty Images


Omicron is posing new challenges to the administration of Covid-19 vaccines globally.

While the Omicron variant is highly transmissible, its severity of illness is significantly reduced compared with the Delta variant.

Discovery Health, South Africa’s largest private health insurance administrator, has found that there is reduced vaccine efficacy, a higher infection risk (particularly for children) and, most notably, a decline in the severity of illness amid the Omicron wave of infections.

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The new variant is driving the country’s entry to the fourth wave.

The latest data, which is based on 211 000 Covid-19 positive results, is preliminary, as it is based on the first three weeks of the Omicron-driven wave in South Africa.

Speaking at a media briefing on Tuesday, Dr Ryan Noach, CEO of Discovery Health, said the analysis of the data showed that the two-dose Pfizer-BioNTech vaccination provided 70% protection against severe complications of Covid-19 requiring hospitalisation and 33% protection against Covid-19 infection during the current Omicron wave.

1.    Reinfection risk: For individuals who have had Covid-19 previously, the risk of reinfection with Omicron is significantly higher, relative to prior variants;

2.    Severity: The risk of hospital admission among adults diagnosed with Covid-19 is 29% lower for the Omicron variant infection compared with infections involving the D614G mutationin South Africa’s first wave in mid-2020, after adjusting for vaccination status;

3.    Children: Despite very low absolute incidence, preliminary data suggests that children have a 20% higher risk of hospital admission in the Omicron-led fourth wave in South Africa than they did during the D614G-led first wave; and

4.    A two-dose Pfizer-BioNTech vaccination provides significant protection against hospitalisation in individuals infected with the Omicron variant.

Over the past month, Discovery Health’s clinical research and actuarial teams have carried out the first at-scale analysis of Omicron’s real-world impact.

They partnered with world-leading researchers from the South African Medical Research Council to provide insights into the effectiveness of the Pfizer-BioNTech vaccine against infections and severe disease linked to Omicron infection.


As of Monday, South Africa had recorded 13 992 new cases. At the time of writing, the country had 174 340 active cases.

A total of 45 101 tests were conducted in the most recent 24-hour period at the time of writing, with a 31% positivity rate.

A further 11 deaths had been recorded.

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On Sunday, the National Institute of Communicable Diseases (NICD) reported 37 875 cases, which included 19 840 retrospective cases and 18 035 new ones.

While these numbers seemed alarming, hospital admissions remained low.

The NICD’s hospital surveillance report showed that there are currently 6 198 Covid-19 patients in hospital. The vast majority of them (5 311) are in general coronavirus wards. A further 420 Covid-19 patients are in intensive care wards and 467 are in high care.

Healthcare workers account for 3% of Covid-19 patients being treated in hospital.


The Omicron variant was first identified in southern Africa in November, triggering hysteria globally, with wealthier nations placing immediate – and irrational – travel bans on South Africa.

 “Superb genetic surveillance by the Network for Genomic Surveillance in South Africa has identified that Omicron infection accounts for over 90% of new infections in the country and has displaced the formerly dominant Delta variant,” said Noach.

The detailed vaccine effectiveness analysis included more than 211 000 positive Covid-19 test results, 41% from adults who had received two doses of the Pfizer-BioNTech vaccine.

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Approximately 78 000 of these positive test results were attributed to Omicron infections between November 15 and December 7, 2021.

“To date, laboratory analysis has provided early insights into potential reduction in the effect of neutralising antibodies against the Omicron variant,” said Noach. “However, there remains an urgent need to establish real-world data on Omicron across all areas of impact. Our research into it is based on a rich and significant sample, and relates directly to the experience of being the first country in the world to face a Covid-19-wave driven by Omicron.”


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