Thread by @vipintukur

#Omicron though the mildest avatar of #SARS2, but is the most transmissible VOC of the SARS2. The original WT variant had an Ro of ~2.5 & the currently dominant variant BA.2 has 12.5! So, there is marked variability in both transmissibility & severity of these VOCs. 1/

Will the next #VOC, whenever it emerges, be the mildest of all variants? A new #Scottish study concludes that it may not be the case, & severity associated with future SARS2 variants is inherently unpredictable. 2/

The principal findings of this study of the relative severity of #COVID19 cases caused by successive SARS2 variant waves in #Scotland was that, #Alpha was associated w/ more severe disease than B.1.177, #Delta was associated with more severe disease than Alpha…….3/

….non-AY.4.2 Delta and AY.4.2 Delta were associated with similar disease severity, & #Omicron was associated with much less severe disease than non-AY.4.2 Delta. 4/

These results were after accounting for comorbidities, changes in treatment & vaccine availability, and robust to epidemic phase bias and the possibility of coincidental SARS2 infection at admission to hospital. 5/

The direction of change in virulence of successively emerging VOCs was inconsistent. This heterogeneity in between variants, coupled w/ independent evolutionary emergence, demonstrates that severity ass w/ future VOCs is inherently unpredictable 6/

medrxiv.org/content/10.110…