Thread
1/6 Important new study from Japan finds that with Omicron, infectious viral loads peak 3-6 days after symptom onset/diagnosis.
So many people are ending isolation & returning to work & school at peak infectiousness. Thanks, @CDCgov.
h/t @gianlucac1
www.niid.go.jp/niid/en/2019-ncov-e/10884-covid19-66-en.html
So many people are ending isolation & returning to work & school at peak infectiousness. Thanks, @CDCgov.
h/t @gianlucac1
www.niid.go.jp/niid/en/2019-ncov-e/10884-covid19-66-en.html
2/6 They looked at 21 cases: 19 vaxxed, 2 unvaxxed, 17 symptomatic, 4 asymptomatic. For the symptomatic, viral loads (by PCR Ct value) were much higher on days 3-6 after symptom onset than days -1 to 2. Furthermore, many samples still had high viral loads on days 7-9. 
3/6 This is very different than what we'd seen with previous variants. Studies by @LucaFerrettiEvo, @DiseaseEcology, & others showed that peak infectiousness previously occurred the day before symptom onset & fell fairly rapidly thereafter. www.medrxiv.org/content/10.1101/2020.09.04.20188516v2 
4/6 Before people start shouting about Ct values measuring dead RNA fragments, note that the researchers cultured virus from these samples, and the results mirrored those for Ct value: peak levels of live virus on days 3-6 & significant amounts of live virus on days 7-9. 
5/6 Will the CDC "follow the science" & revise their 5-day, no-exit-test isolation period in light of these results? Or was that guideline based entirely on political & economic considerations (i.e. the desires of the wealthy & well-connected political donors)? Take a guess.
6/6 I know @michaelmina_lab discussed the tendency for infectiousness to peak later (relative to symptom onset) in a population with widespread immunity compared to a naive pop, but I can't find the tweet. This + short incubation period may largely explain this study's findings.
7/ Adding this from @LazarusLong13: Taiwan rejects shortening of the 10-day isolation period based on viral load measurements (based on Ct value). They didn't culture to detect live virus, but their Ct results match very well w/the Japan study.
8/ Who has more credibility and a better track record when it comes to Covid, the U.S. CDC or Taiwan's CECC? 🤔🤔
Mentions
See All
Zeynep Tufekci @zeynep
·
Jan 9, 2022
This is interesting work, but I don’t know why authors bin the results (3-6 days) instead of just giving us the exact days. Also, why don’t we have our own studies like this? This is exactly what we need to know. And: I suspect this distribution may be bimodal by vax/symptom.