Why Is Omicron Less Lethal?

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Last month, We have discussed how to trace the impacts of Omicron on Colab (Yiu, 2021), as we initially observed that the Omicron variant seemed to spread faster, but it was not as lethal as Delta. It might turn the deadly pandemic to a mild common cold.

On January 3, the WHO (initially) confirmed that Omicron causes milder symptoms (Farge & Roy, 2022). There have been not less than six academic studies that have found that “Omicron does not damage people’s lungs as much as the Delta…”.

Among them, a study by Deenan Pillay, professor of virology at University College London, found that “[Omicron] seems to be more able to infect cells in the upper respiratory tract-the throat, so it multiplies more easily in the cells there than in the cells deep in the lungs.” (Tapper, 2022)

Another study conducted by the Hong Kong University School of Medicine team also found that “Omicron SARS-CoV-2 infects and multiplies 70 times faster than the Delta variant and original SARS-CoV-2 in human bronchus, which may explain why Omicron may transmit faster between humans than previous variants. Their study also showed that the Omicron infection in the lung is significantly lower than the original SARS-CoV-2, which may be an indicator of lower disease severity. This research is currently under peer review for publication.” (HKU, 2022)

It may be a natural evolution pathway for virus to spread fast and infect more people rather than killing them all. But it still requires more and longer data series to confirm. As a caveat, even if the death rate of Omicron may be lower, but when the number of the infected is increasing tremendously, a tiny death rate can still imply a large number of deaths.

ND/NC

Figure 1 shows the New Deaths to New Confirmed Cases Ratio (ND/NC) in South Africa and the UK before and after the spread of the Omicron variant in late 2021, it shows that the Omicron is less lethal.

The charts are updated to January 4, 2022. The figure on the left shows that the number of newly confirmed cases per million people in the UK (red line) has surged from less than 500 per day to more than 4000 per day per million people. However, the middle chart indicates that the death rate (mainly caused by the Omicron variant after December 2021) in the UK does not seem to rise as strong as the number of confirmed cases (about 5 people/per million people per day). It is much lower than that in the first and second wave of the pandemic as shown in the chart (about 15 and 25 people/per million people per day). The figure on the right shows the ratio of newly confirmed deaths to newly confirmed cases (ND /NC), which can be a proxy of tracking the lethality of the virus. The ratio in the United Kingdom since December 2021 is significantly lower than that in the first and second waves. The ratio in South Africa has also fallen to below 0.05 in recent days.

References

Farge, E. & Roy, M. (2022) WHO sees more evidence that Omicron causes milder symptoms, Reuters, January 4. https://www.reuters.com/business/healthcare-pharmaceuticals/who-sees-more-evidence -that-omicron-affects-upper-respiratory-tract-2022–01–04/?utm_campaign=trueAnthem%3A%20Trending%20Content&utm_medium=trueAnthem&utm_source=facebook&fbclid=IwAR1MvBc17riXkXqmpgGSh9f93XmaXkXqmpgGSh9f93XmaXkXqmpgGSh9f93Xma9_ewD

HKU (2021) HKUMed finds Omicron SARS-COV-2 can infect faster and better than Delta in human bronchus but with less severe infection in lung, News, December 15. https://www.med.hku.hk/en/news /press/20211215-omicron-sars-cov-2-infection

Tapper, J. (2022) New studies reinforce belief that Omicron is less likely to damage lungs, The Guardian, January 2. https://www.theguardian.com/world/2022/jan/02/new-studies-reinforce- belief-that-omicron-is-less-likely-to-damage-lungs

Yiu, C.Y. (2021) Trace the Impacts of Omicron on Colab, Medium, December 15. https://ecyy.medium.com/trace-the-impacts-of-omicron-on-colab-da2e96aa360c