Last friday we sent to @ECDC_EU and @EU_Commission our report on the subsitution process of B.1.1.7 in Catalonia. An increase in transmissibility of around 50% is not translated into an important increase in the effective reproductive number. Open thread with ideas of report. 1/ 
The previous graph shows how B.1.1.7 went from being a low fraction of the cases to reaching 80% of the cases. During January and February important restrictions were in place in Catalonia. Rt went from roughly 0.8 to 0.9 during most of the substitution process 2/
A naive interpretation of the substitution using SIR models without specific social interaction nor space produces erroneous results where an increase in transmissibility is translated directly into an increase in Rt. Here the classical picture 3/
This is not the proper picture to understand the substitution process. The increase in transmissibility and in secondary attack rate leads one to one increases in Rt in the absence of social distance measures which affect how the virus jumps between different social groups 4/
A more realsitic model is one where there are interactions at different distances in the social-interaction space. The properties of this connections modulates completely how trasnmissibility is transformed into an increase in the effective reproductive number 5/
If interactions are heavily restricted to people very close in your social space, this is is the typical substitution process that we observe (right) in a toy model developed in the group to explain the process observed in Catalonia. Left no restrictions, right restrictions 6/
The scenarios without restriction and with restrictions produce the same substitution curve but when restriction are applied, the increase in transmissibility is not observerd in the effective reproductive number. Here we show how the subsitution is the same in both situations 7/
The subsitution of the new variant is produced, showing a 50% increase in transmissibility, but the epidemics remains perfectly under control. You can read all the details here: biocomsc.upc.edu/en/shared/2021… All the reports here: biocomsc.upc.edu/en/covid-19/da… 8/
The key open question is to know the level of restrictions required to observe this control depending on socio-economic (and other) factors. Work coordinated by @SergioAlonsoMun and @prats_clara and 9/
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