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% per-day growth rate of Omicron


On 25 November, South Africa announced that it was tracking a new variant, B.1.1.529/Omicron, and shared the following:

  • New variant detected in South Africa (lineage B.1.1.529) with high number of mutations, which are concerning for predicted immune evasion and transmissibility
  • B.1.1.529 genomes produced from samples collected 12-20 Nov from Gauteng, SA (n=77), Botswana (n=4) and Hong Kong (n=1, traveler from SA)
  • B.1.1.529 can be detected by one particular PCR assay (before whole genome sequencing)
  • Early signs from diagnostic laboratories that B.1.1.529 has rapidly increased in Gauteng and may already be present in most provinces
  • Mutation profile predicted to give significant immune evasion and enhanced transmissibility

See also these three assessments by the UK HSA, Belgian NRL, and WHO respectively.

One way to assess the transmissibility of a new variant in a way that accounts for both its inherent transmissibility and its ability to evade preexisting immunity is to examine its growth rate over other variants. A 26 November estimate by the Belgian NRL finds that the growth rate of Omicron is ~38% per day compared to Delta — however, some have characterized this estimate as “implausibly high”.

[Short-fuse] What will the % per-day growth rate advantage of Omicron relative to Delta be based on information available as of 23 December?

This will resolve on the basis of the percent per-day growth rate advantage that is estimated for the Omicron variant relative to Delta, according to the credible estimate that is most recent as of 6AM EST on 23 December 2021. This estimate should preferably be made in a published study, assessment, or pre-print — so long as such an estimate includes data through at least 13 December. If such an estimate cannot be found, then estimates made by individual researchers deemed trustworthy by the question author, like Tom Wenseleers, Trevor Bedford, or Theo Sanderson, can be considered if they include data through at least 13 December.

A negative growth rate (<0%) would indicate that Omicron is less transmissible than Delta.

Thank you to Nathan Young, Clay Graubard, David Manheim, Philipp Schoenegger, and Edward Saperia for their question suggestions and input.

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