Encouraging preliminary data shows Omicron less likely to cause serious illness than past, dominant SARS-CoV-2 variants

Authors
Shirley Collie (Chief Healthcare Analytics Actuary, Discovery Health), Tommy Chen (Actuary, Discovery Health) and Michael Cohen (Actuarial Analyst, Discovery Health)

• Important: These insights relate to data from the first three weeks of the Omicron-driven wave in South Africa. Therefore, these results are preliminary and may change as the wave continues. This data is also confounded by various factors, including high seroprevalence (the percentage of individuals in a population who have antibodies) of COVID-19 antibodies in the South African population, which may contribute to the lower disease severity recorded as being linked to the Omicron variant.

The Omicron variant of SARS-CoV-2 was first identified in Southern Africa in November 2021, brought to the attention of the world by scientists in South Africa and Botswana and declared a 'variant of concern' by the World Health Organization shortly afterwards.

South Africa experienced rapid Omicron community spread (initially concentrated in the Gauteng province). Over December 2021 and into early 2022, the highly transmissible Omicron variant replaced the formerly dominant Delta variant and drove an exponential rise in COVID-19 cases in South Africa's fourth wave of infection.

Given the increased transmissibility of the Omicron variant compared to previous COVID-19 variants, it quickly became important to predict the severity of illness this variant might cause and the resulting COVID-19 hospital admission rate that could result during the fourth wave.

Dealing with the health information of more than 3.7 million people, Discovery Health, has extensive claims data and private health system use data and is uniquely positioned to generate at-scale real-world insights into the impact of COVID-19.

To this end, we investigated the early data available on disease severity linked to Omicron infection in a group of 380 430 members of medical schemes administered by Discovery Health.

This research into disease severity during the Omicron-led fourth wave was carried out as part of a wider analysis - the first at-scale, real-world analysis of Omicron's impact, as reported on here .

1. This wider analysis includes Discovery Health's research on the effectiveness of two-dose Pfizer-BioNTech vaccination in preventing severe disease and hospitalisation as a result of Omicron infection. This work has been carried out by Discovery Health's actuarial team in collaboration with leading scientists at the South African Medical Research Council.

2. Further, on 29 December 2021, the New England Journal of Medicine published our Correspondence: " Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa " detailing the research carried out in partnership with the South African Medical Research Council.

Increased transmissibility of Omicron variant evident among medical scheme members

From 15 November 2021, there has been a significant increase in the number of confirmed COVID-19 infections among members of medical schemes administered by Discovery Health.
By 10 December 2021:

• 43% of COVID-19 tests undertaken returned positive - a test positivity rate like that seen at the peaks of South Africa's second and third waves of infection earlier in the year.
• The seven-day rolling average of daily new cases was 2 984 for medical scheme members (and 15 043 nationally), showing an ongoing upward trend. This case rate surpassed the peak seven-day rolling average of daily new cases seen in the first and second waves.

We set out to investigate how the severity of clinical outcomes recorded during the Omicron period of COVID-19 infection compared to outcomes recorded in previous waves of COVID-19 infection which were driven by earlier SARS-CoV-2 variants. Our investigation considered only adult medical scheme members (aged 18 years and older).

Our methodology

We assessed the risk of admission following confirmed COVID-19 infection, using a Cox proportional hazard model, and adjusting for:

• Vaccination type and status (e.g., Johnson & Johnson or Pfizer COVID-19 vaccine, number of doses, and time since last dose)
• Age (<40, then in 10-year bands up to age >=80)
• Sex
• Observation times post-PCR testing (in days)
• Number of Centers for Disease Control and Prevention (CDC) risk factors (0,1,2,3+)¹ the member has
• Dominant variant on the member's infection date
• Last documented infection from (likely) previous dominant variant

The following table shows the start and end dates selected for the dominant period of each variant of concern for the purposes of this comparison. These periods are established through research by experts involved in the Network for Genomic Surveillance in South Africa .

Periods over which four distinct SARS-CoV-2 variants were dominant in South Africa

*This variant was first reported to the World Health Organization on 24 November 2021; however, detection of first infections of the variant date back to 9 November 2021.

We assessed and interpreted the 'dominant variant as at infection date' coefficient from the Cox proportional hazard model to assess the relative risk of admission across different periods of infection.

Using hospital admission rates as a proxy for the severity of each variant of the SARS-CoV-2 virus dominant at particular periods, it is apparent that (up to 10 December 2021) the severity of disease caused by the Omicron variant was lower than that documented in South Africa's first, second and third waves, when D614G (the ancestral variant), Beta, and Delta, respectively, were the predominant circulating variants.

The data shows:

• There was a 12% higher relative risk of admission for the Beta-led wave relative to the D614G-led first wave
• There was a 6% lower risk of admission during the Delta-led wave relative to the D614G-led first wave
• There is currently a 29% lower risk of admission during the Omicron-led wave of infection relative to the D614G-led first wave

Relative risk of admission to hospital for COVID-19-positive patients for each SARS-CoV-2 variant dominant over time in South Africa

As mentioned, these are early - so preliminary - insights and the outlook may change over the course of the fourth wave.

That said, all in all it is highly encouraging that this early analysis shows a lowered hospital admission risk for adult medical scheme members who contract COVID-19 in the fourth (Omicron-led) wave of infection in South Africa, relative to past waves of infection. The Omicron variant, it would seem; therefore, does not cause higher levels of severe illness, despite its heightened transmissibility.

It is very important to note that the lower relative admission risk experienced in the Omicron-led fourth wave may well be linked to the lowered pathogenicity (the potential ability to produce disease) of the Omicron variant. However, the lowered trend toward admission is, by now (almost two years into the pandemic), also very likely simultaneously fuelled by protection from serious illness after being infected before (and because of natural immunity gained after COVID-19 infection).

From 2 March 2020 to 14 November 2021, 437 592 cases of COVID-19 infection were recorded within the 3.7-million-member Discovery Health medical scheme member base. Many studies around the world have shown higher seropositivity rates than that indicated based on national surveillance statistics. Locally, a South African study published in December 2021 estimated that 95% of COVID-19 infections were not reported to national surveillance. The extent to which underlying seroprevalence levels of SARS CoV-2 antibodies within the Discovery Health medical scheme member base contribute to these observations is unclear and complex to investigate.

All in all, we will continue to monitor these trends in the coming weeks, through to the end of the fourth wave of infection and report back on our findings.

Appendix 1

The following list of comorbidities (presented in alphabetical order) has been adapted from the Prescribed Minimum Benefits Chronic Disease List (CDL) and the Centers for Disease Control and Prevention's list of conditions associated with increased risk of severe COVID-19 .

Please email media_relations_team@discovery.co.za to request any updated data available since publication and to obtain any further context required.

Did you find this post interesting?

You may also be interested in reading our related post - our press release summarising our broader analysis of the Omicron variant with, predominantly, coverage of the way in which the two-dose Pfizer-BioNTech vaccination provides 70% protection against severe complications of COVID-19 requiring hospitalisation, and 33% protection against COVID-19 infection, during the current Omicron wave.

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