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Omicron transmission risk over 2 times of Delta, in fully vaccinated (Allen 2022 preprint)

Some days after blogging on not finding any publications about Omicron transmission in the context of the available vaccine products, I came across an Nature news article on Omicron transmission in UK.

Its about Hester Allen et al 2022, a preprint study that attempts to quantify the effects of vaccination series on prevention of severe COVID and on transmission, and the differences between Delta and Omicron SARS-CoV-2 variants. As it is a epidemiology related preprint, it has not been peer-reviewed and so it may be further edited.

The full title is "Comparative transmission of SARS-CoV-2 Omicron (B.1.1.529) and Delta (B.1.617.2) variants and the impact of vaccination: national cohort study, England" and the authors are reported to be part of UK Health Security Agency. graph comparing Delta and Omicron transmission in vaccinated In people with 3 vaccinations (2021 generation), the transmission of Delta from an infected family member was 63% less likely than transmission of Omicron variant virus. Image copyright (C) C. Pohjanraito 2022

Some key numbers from the article

  • Between 05 and 11 December 2021
  • 23,667 Omicron and 59,031 Delta cases
  • interval of exposure to a secondary case 4 days for Delta, and 3 days for Omicron
  • Secondary Attack Rate: Omicron 15.0% vs 10.8% Delta cases (unadjusted)
  • Omicron at worst 2 times more likely to infect contacts (Risk Ratio of transmission O vs D: 2.43)

Copyright Casimir Pohjanraito 2021

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