Thread by @vipintukur

Viral dynamics & duration of PCR positivity of the #Omicron variant

In this study, longitudinal RT-qPCR tests collected between July 5th 2021 & January 10th 2022. This included 97 Omicron infections and 107 confirmed Delta infections 1/

Here are trajectories from individuals detected ≤1 day or ≥2 days since a previous negative or inconclusive test. 2/

Omicron infection duration was similar to Delta (both ~10 days), but Omicron infections had lower peak viral loads (higher peak Ct values). 3/

There is more variability in estimated ‘proliferation times’ – that is the delay from infection to reaching peak Ct. Plot shows individual-level posterior mean estimates (Red:Omicron, Blue: Delta). 4/

This reflects that some Omicron infections with low viral load for a few days prior to growth, possibly reflecting suppression via immunity or different compartmentalization in the respiratory tract, while others grow rapidly. 5/

Was there some impact of ore-existing immunity on Omicron’s growth?

Yes, may be. As most of these individuals are vaccinated and many were boosted before the rise of Omicron. 6/

Key takeaways:

1- ~50% of individuals have low Cts ≥5 days post detection, even in this highly-boosted population

2-Peak viral load, proxied by Ct values, is lower, and peaks no sooner, than for Omicron than Delta. 7/

3-So Omicron’s increased infectiousness doesn’t seem to be through higher viral load 8/

Conclusions: While Omicron infections feature lower peak viral RNA & a shorter clearance than Delta infections, it is unclear to what extent these diff are attributable to more immunity in largely vaxxed population or intrinsic features of Omicron 8/

medrxiv.org/content/10.110…

@PeacockFlu has some interesting explanation on the lower viral load for tje Omicron to efficiently infect a greater number of cells in the upper respiratory tract at even a lower infectious dose

https://twitter.com/vipintukur/status/1477336778038079488?s=21