Our preprint on infectious viral load in unvaccinated & mRNA vaccinated patients infected with #SARSCoV2 WT, #Delta & #Omicron is out! #CovidVaccine #COVID19 What did we find? 1/ medrxiv.org/content/10.110…
We found only a low correlation between RNA genome copies & infectious viral titers as determined by focus forming assay for #SARSCoV2 Wt, #Delta infection & Delta vaccine breakthrough - means, RNA viral load does not tell so much about infectiousness 2/
Next, we quantified infectious viral particles in early-pandemic #SARSCoV2 (before any variant of concern, "pre-VOC") & #Delta in unvaccinated individuals: we found higher RNA copy numbers in pre-VOC than Delta, but more infectious viral load in Delta 3/ 
Also, infectious viral load was higher for Delta 3-5 days after symptoms, while similar to per-VOC #SARSCoV2 during first 0-2 days. More & longer infectious virus shedding could explain higher transmissibility of Delta. Next, we looked at Delta vaccine breakthrough infections 4/
RNA copies did not differ much between Delta in unvaccinated vs vaccinated individuals, but viral load shedding was much lower (0.68 log) & declined faster in breakthrough. However, half of the vaccine breakthrough samples still had infectious virus at 5 dpos! 5/
Last, we compared RNA copies & infectious viral titers in Delta & Omicron breakthrough infections & did not find differences in quantity. Although Omicron is highly transmissible even from vaccinated index cases, it does not seem to be due to higher viral loads compared to Delta!
Great work from a fantastic team led by @OlhaVPuhach & @BenjaminMeyer85 & many other colleagues at @Hopitaux_unige @MIMOL_UNIGE @unige_en @gcevd funded by @snf_ch @nrp78_covid19
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