Thread by @mugecevik

Very interesting analyses about the virology of #Omicron, which may explain the faster spread of this variant.

According to a new lab study, Omicron infects & multiplies ~70x faster than the Delta variant and the wild type SARS-CoV-2 in the human bronchus, but not in the lung.

In this ex vivo study (press release), Michael Chan, Malik Peiris & John Nicholls et al. @hkumed show that at 24h after infection Omicron replicated ~70x faster than Delta in bronchus. Interestingly, it replicated ~10x less efficiently in the lung tissue. hkumed.hk/96b127/

Another analysis by @BalazsLab also supports these findings. In this lab study w/ pseudoviruses, Omicron showed greater ability to infect cells than other variants, which was ~ 4 times more infectious than the original strain, also more than Delta. medrxiv.org/content/10.110…

These preliminary laboratory analyses indicate that;
📍Omicron is significantly more transmissible than delta
📍Less efficient replication in the lungs may suggest lower severity, but severity in humans is not determined only by virus replication but also the host immune response

Important to note that first study is an ex vivo work, meaning that human tissue is used to look at virus replication in the lab. So, this is not a definitive but supportive finding & needs to be confirmed by clinical data as host immune response is absent in these studies.

Lay summary: These results indicate inherent transmissibility & replication advantage of Omicron (in addition to immune evasion) compared to delta. It also explains why it spreads quickly and outcompeted delta in SA, which fits w/ modelling assumptions.

https://twitter.com/mugecevik/status/1466845357686640640?s=20

For those asking whether this is good/bad news, simple answer: I don't know. While omicron may infect the lung cells less efficiently, a higher viral load may worsen immune response. We discussed the pathogenesis w/
@KindrachukJason @KrutikaKuppalli bmj.com/content/371/bm…

The only thing I am sure of is that omicron will spread so quickly through the population, making it likely impossible to contain even with the most stringent measures & giving us very little time over the next few weeks. So get your vaccines & boosters!

https://twitter.com/mugecevik/status/1468518680157999106?s=20