Our new preprint on the spread of the #SARSCoV2 variant Alpha in Geneva, Switzerland, and Beta in South Africa is online. We used clinical and epidemiological data to better understand the mechanisms that lead to a transmission advantage of the #VOCs. 1/8 doi.org/10.1101/2021.0… 
When analyzing viral load in 950 individuals, we found that Alpha infections exhibit a higher viral load and longer viral shedding compared to non-VOC. 2/8
We then used a transmission model to study the following potential mechanisms that result in a transmission advantage: i) increase in transmissibility, ii) increase of infectious duration, and iii) immune evasion. 3/8
We estimated that Alpha is either associated with a 37% (95% CI: 25-63%) increase in transmissibility or a 51% (95% CI: 32-80%) increase of the infectious duration compared to previously circulating variants, or a combination of the two mechanisms. 4/8
Assuming 50% immune evasion for Beta, we estimated a 23% (95% CI: 10-37%) increase in transmissibility or a 38% (95% CI: 15-78%) increase of the infectious duration, i.e., less than we estimated Alpha. 5/8
However, our analysis suggests that Beta might be expected to outgrow Alpha in regions where the level of naturally acquired immunity against previously circulating variants exceeds 20% to 40%. 6/8
With Delta, we have a new player in the game and it will be interesting to follow how the competition between these #VOCs turns out in settings with different levels of naturally acquired and vaccine-elicited immunity. 7/8
Thanks to @EckerleIsabella, @rjlessells, @Tuliodna, @firefoxx66, @richardneher and many others who have been involved in this study. @ISPMBern @Hopitaux_unige @snsf_ch @EpiPose 8/8
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