Thread by @EckerleIsabella

Our paper on infectious viral load in vaccinated & unvaccinated individuals infected with ancestral, #Delta or #Omicron #SARSCoV2 #COVID19 published today in
@NatureMedicine - what did we find? A 🧵1/
nature.com/articles/s4159…

We assessed infectious viral particles & RNA viral load from nasopharyngeal swabs of 565 #SARSCoV2 infected individuals in the first 5 days post symptom onset over several waves: 2020 ("pre-VOC", before the rise of #variants of concern), #Delta in 2021 & #Omicron in 2022. 2/

First of all, we found a rather low correlation between viral RNA copies and infectious viral titers & no correlation of infectious viral load with age or sex. Infectious viral load in unvaccinated individuals was higher when infected with #Delta than with pre-VOC #SARSCoV2 3/

Next, we have investigated the effect of #vaccination (2 doses mRNA) on infectious viral load: In vaccinated individuals with a Delta breakthrough infection, infectious virus was almost 5-fold lower & was cleared more rapidly than in the unvaccinated with Delta 4/

For Omicron BA.1 infections, we have investigated infectious viral load for unvaccinated, 2x vaccinated & 3x vaccinated individuals. In 2x vaccinated individuals with a breakthrough infection, Omicron (while being highly contagious) had lower infectious viral load than Delta! 5/

Next, effect of #vaccination (2x or 3x) on infectious viral load in #Omicron BA.1 infections: Individuals with 2x mRNA vaccine had comparable infectious viral load to unvaccinated. But with additional (booster) dose we saw a more than 5-fold reduction in infectious viral load! 6/

Our data demonstrate that 1) measuring viral RNA (Ct values/copy numbers) are not the full story when it comes to viral load 2) it's important to asses infectious (culturable) virus to better understand viral shedding profiles 3) vaccination impacts infectious viral load 7/

Public health impact of our findings: vaccination can reduce infectious viral load, likely leading to lower onward transmission. These findings underscore the benefit of #vaccination on #SARSCoV2 circulation beyond individual protection from severe disease #SARSCoV2 #COVID19 8/

The work was a huge team effort of our hospital @Hopitaux_unige @FJacque1 @LaurentKaiser1 @GenecandC, the emerging virus team @UNIGEnews @unige_en @gcevd @MIMOL_UNIGE @KennethAdea, led by @OlhaVPuhach & Centre for Vaccinology @BenjaminMeyer85, funded by @snf_ch @nrp78_covid19 9/9

Note: we did not have information on prior infections in the individuals tested & we did also not assess the effect over different time points after having received the booster (Switzerland introduced boosters rather late). Hopefully we will be able to this in the future.