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.

There is substantial concern that Omicron might be more transmissible than Delta.

One way to assess the transmissibility of a virus is to examine its basic reproduction number (R0), which Delamater et. al (2019) define as:

an epidemiologic metric used to describe the contagiousness or transmissibility of infectious agents. R0 is affected by numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission and, therefore, is usually estimated with various types of complex mathematical models...R0 is not a biological constant for a pathogen, a rate over time, or a measure of disease severity, and R0 cannot be modified through vaccination campaigns. R0 is rarely measured directly, and modeled R0 values are dependent on model structures and assumptions.

Again, note that that R0 calculation refers to transmission in a theoretical population where no one is vaccinated and no one has already had the disease. This question is thus trying to forecast the inherent transmissibility of Omicron, irrespective of its ability to evade preexisting immunity.

What will be the R0 of the Omicron variant according to the mean estimate of the first relevant systematic review?

This will resolve on the basis of the mean R0 that is estimated for the Omicron variant according to the first credible systematic review that estimates this value. Such a systematic review should be peer-reviewed and should incorporate R0 estimates from at least 3 studies. An example is the systematic review by Liu and Rocklov (2021):

In this study, we review the basic reproductive number (R0) of the Delta variant … We identified five studies, which estimated the basic reproductive number for Delta. Table 1 shows that the basic reproductive number for Delta ranged from 3.2 to 8, with a mean of 5.08.

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