We hear often about how delta is more transmissible, but we don't hear much about why that's the case or how that impacts exposure risk. A new study by Li and colleagues is out on Virological that provides some insight:https://virological.org/t/viral-infection-and-transmission-in-a-large-well-traced-outbreak-caused-by-the-delta-sars-cov-2-variant/724 …
-
Show this thread
-
There's been a lot of breathless news coverage about delta and it's mostly focused on increased transmissibility (and maybe pathogenicity). VOCs aren't just inherently more transmissible (or more pathogenic). There must be a mechanism that underlies increased transmission.
4 replies 96 retweets 588 likesShow this thread -
Some hypothetical mechanisms include: -Increased fitness (more shedding) -Increased infectivity (better at infecting host cells ie tighter receptor binding) -Longer period of contagion (shed virus for longer) -Increased environmental stability (more tolerant to temp/humidity/etc)
4 replies 97 retweets 609 likesShow this thread -
This study attempted to address this in quarantined close contacts of confirmed cases. These people were tested daily by PCR, which allowed the investigators to determine the course of infection: longitudinal viral loads and time from exposure to positivity and symptoms.
2 replies 67 retweets 471 likesShow this thread -
The findings are quite striking. This shows that: -People infected with delta test positive more quickly following exposure, suggesting more rapid viral growth. -The viral loads (by PCR Ct) are 1000 times higher in delta when first detected.pic.twitter.com/ROZZzWwqhB
32 replies 858 retweets 1,636 likesShow this thread -
This suggests that the delta incubation period is reduced compared to the prior viruses. Also, people infected with delta are shedding a shit-ton more virus than those from earlier variants. This certainly explains delta's increased transmissibility.
26 replies 564 retweets 1,565 likesShow this thread -
If people are shedding 1000X more virus, the probability that a close contact will be exposed to an infectious dose is much higher. If people become contagious more quickly after exposure, they can have more opportunity to infect others.
13 replies 342 retweets 1,146 likesShow this thread -
Now, I've also seen a lot of
DELTA IS MORE AIRBORNE!!!!!1!!!
commentary, which is neither helpful nor accurate. A virus is a physical structure that still has to obey the laws of physics. It can't become "more airborne"...and I'm not even sure what that means.33 replies 184 retweets 1,191 likesShow this thread
atmospheric dwell time is nonlinear in particle size, so if delta biases to smaller virions it could have the effect of an increased viral load in the air, for longer. images i’ve seen indicate a significant dispersion in virion sizepic.twitter.com/xuj7g8xqDn
Loading seems to be taking a while.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.
