Epidemic mannequin for estimating relative transmissibility and immune escape of SARS-CoV-2 Omicron variant in South Africa

As of December twenty eighth, 2021, the Omicron variant of extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been detected in additional than 110 nations and territories worldwide. SARS-CoV-2 is the causal agent of the coronavirus illness 2019 (COVID-19) pandemic, which has ravaged human lives and the worldwide financial system.

Study: Preliminary modeling estimates of the relative transmissibility and immune escape of the Omicron SARS-CoV-2 variant of concern in South Africa. Image Credit: anushkaniroshan/ShutterstockExamine: Preliminary modeling estimates of the relative transmissibility and immune escape of the Omicron SARS-CoV-2 variant of concern in South Africa. Picture Credit score: anushkaniroshan/Shutterstock

The Omicron variant was first found in South Africa and was formally named a variant of concern (VOC) on November twenty sixth, 2021. Scientists are working extensively to grasp the properties of this new variant to tell public well being measures appropriately.

A brand new examine, printed on the medRxiv* preprint server, developed a stochastic, multi-strain, compartmental epidemic mannequin to estimate the relative transmissibility and immune escape capability of the Omicron variant.


The widespread neighborhood transmission of Omicron was first noticed in South Africa – notably within the province of Gauteng. The nation had skilled a extreme wave of the Delta VOC earlier within the 12 months; nevertheless, instances and deaths had been declining since August 2021. As of late November, solely 24% of the inhabitants of South Africa was totally vaccinated – suggesting that the mitigation of the Delta wave was primarily pushed by excessive ranges of pure immunity throughout the inhabitants.

In November, the speedy rise of instances indicated that the brand new variant had a major development benefit over the Delta VOC. Primarily based on early statistical evaluation, scientists said that the quick unfold of Omicron might be defined by elevated transmissibility, immune escape, or a mixture of each.

A brand new examine

Within the present examine, scientists developed a multi-strain, stochastic, compartmental epidemic mannequin for South Africa to determine a few of the options of the brand new variant suitable with epidemiological observations. The inputs to the mannequin are a number of essential elements, reminiscent of demographics, age-stratified contact patterns, non-pharmaceutical interventions (NPIs), vaccine rollout, and many others. Subsequently, a multi-stage calibration was carried out by making use of an Approximated Bayesian Computation (ABC) methodology.

Scientists explored a parameter house outlined by combining the relative transmissibility of the Omicron variant in comparison with the Delta VOC. Additionally they studied the immune escape of Omicron with respect to each naturally acquired immunity and vaccines. The following step was to acquire a joint posterior distribution of those parameters, suitable with the variety of confirmed instances till December thirteenth, 2021.

Most important findings

The outcomes obtained on this examine are according to early statistical evaluation stating that Omicron can reinfect people at charges larger than earlier VOCs, and vaccines may be much less efficient in opposition to an infection. Researchers obtained a joint posterior distribution for the relative transmissibility with respect to Delta VOC and immune escape of the Omicron variant.

One problem with the prevailing information is that it doesn’t permit to determine each parameters uniquely, due to which scientists outlined a area the place a big spreading benefit may be compensated by a restricted immune escape and vice versa.

One other attention-grabbing remark was that the assumed technology time of Omicron had a major affect on the outcomes. Quick technology occasions (i.e., 3.5 days) with respect to the Delta variant (i.e., 5.5 days) shifted the joint posterior distribution to a area with smaller values of transmissibility benefit for Omicron. The findings obtained on this examine reinforce the speedy unfold of the Omicron VOC, which was the dominant circulating pressure for the reason that second week of November.   


The primary limitation is with respect to the compartmental construction, which is comparatively easy and doesn’t account explicitly for asymptomatic transmission and completely different levels of illness severity. Secondly, the info had been additionally restricted on the precise variety of completely different vaccines administered. Thirdly, additional mutations and divergence of Omicron may have an effect on a few of these values. Lastly, the mannequin didn’t account for geographical heterogeneity.


The outcomes introduced on this examine verify that extra information is important to estimate the important thing traits of the Omicron variant. Nevertheless, the preliminary evaluation means that the Omicron variant may additionally trigger new pandemic waves in areas with excessive assault charges from earlier strains and/or vaccination charges. Knowledge on the severity of the Omicron variant, in comparison with the Delta VOC, might be important to gauge the influence on the healthcare techniques of nations affected by an increase in instances pushed by the Omicron variant.

*Essential discover

medRxiv publishes preliminary scientific experiences that aren’t peer-reviewed and, subsequently, shouldn’t be considered conclusive, information scientific observe/health-related habits, or handled as established info.

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