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Jan 28 • 5 tweets • 3 min read
After posting this, I realized that BA.2 has a ways to go before it reaches the transmissibility of foot and mouth disease, an airborne livestock illness. How contagious is foot and mouth disease? Well... 1/4
It has been known to spread through the air, from one farm to another, over distances of HUNDREDS OF KILOMETERS. You might think I'm joking. I'm not joking. 2/4
acp.copernicus.org/articles/3/210…
I haven't investigated this issue closely, but it's believed that foot and mouth disease from farms in Brittany, France, was carried by the wind across almost the entire English Channel and infected livestock on the Isle of Wight. 3/4 daera-ni.gov.uk/articles/foot-…
I can see it now, in 2025: epidemiologists watching transoceanic wind currents to predict the spread of the Omega variant from continent to continent. 4/4
h/t to @jmcrookston, @jljcolorado, & co. who put together this phenomenal historical paper on the history of airborne disease transmission, one of the best papers I've ever read, & one I keep coming back to. I first heard of foot & mouth disease from here. papers.ssrn.com/sol3/papers.cf…

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More from @LongDesertTrain

Ryan Hisner Profile picture
Jan 28
A thread of BA.2 updates.

BA.2 continues to do its thing in Denmark. The two most recent days of sequencing (January 20 & 21) recorded 74.2% BA.2 (285 of 384 cases). 1/9 Image
The exponential increase in the proportion of BA.2 cases continues in the UK.

The apparent slowdown in growth in the past several days is entirely due to 0 of 8 sequences being BA.2 over the past four days & should therefore be ignored. 2/9 Image
Similar exponential increase in the percentage of BA.2 cases in the US.

Again, the illusory plunge over the last five days is entirely due to a very small number of sequences and should be ignored. 3/9 Image
Read 10 tweets
Ryan Hisner Profile picture
Jan 27
In the US, she would have been back at work/school and infecting others for four days now. 1/5
This woman was triple-vaccinated, by the way. As with Delta, people with breakthrough Omicron infections are approximately as infectious as unvaccinated cases and can be superspreaders. 2/5
Reminder that the CDC decision to shorten the isolation period was exactly backward: the peak infectious period with Omicron is several days later relative to symptom onset than with previous variants. 3/5
Read 5 tweets
Ryan Hisner Profile picture
Jan 25
As Omicron has washed over the US, infecting perhaps 25% of the population already & likely to reach 40% by mid-February—see thread by @trvrb below—it has driven down almost all other respiratory pathogens, with one curious exception I’ll get to later. 1/9
This is not entirely unexpected. Viral infections trigger both innate and adaptive immune responses that can prevent infection by other viruses. Behavior changes likely contribute to this pattern as well. 2/9
There have been some claims that rhinovirus infection protects against SARS-CoV-2 infection. As you can see in the graph below, SARS-CoV-2 and RV prevalence seem almost perfectly inversely related in recent months. 3/9 news.yale.edu/2021/06/15/com…
Read 9 tweets
Ryan Hisner Profile picture
Jan 23
No one seems to know what BA.2 means for the world. I'm not aware of any studies on it, but I hope they come out soon. It seems apparent BA.2 will become dominant everywhere before long—as it already has in Denmark.

🧵 of graphs comparing BA.1 & BA.2 in various countries
1/16
Of all the countries with decent genetic surveillance, Denmark has the highest proportion of BA.2. 2/16
According to the Outbreak numbers compiled using @GISAID data, January 12 was when BA.2 surpassed 50% of all cases in Denmark, with 480/955 cases. 3/16
Read 16 tweets
Ryan Hisner Profile picture
Jan 9
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
niid.go.jp/niid/en/2019-n…
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. medrxiv.org/content/10.110…
Read 8 tweets
Ryan Hisner Profile picture
Jan 9
Hard to believe Walensky said this out loud—apparently intentionally.

I'm pretty sure if Trump had said this, all the major media would've been in an uproar for days or weeks—and rightfully so. Why is this not a major story? Has she apologized?
I thought this was a joke tweet, but I followed the link, and there it is, on page 5 of the CDC's 152-page list of "Conditions contributing to deaths involving COVID-19" through Dec 5, 2020: bird fancier's lung.
Reminder that there are people out there who have 4+ comorbidities entirely because they had Covid & never got better. If Omicron kills one of them, what fraction of a "healthy death" is their life worth?

50%?
25%?
10%?

Someone needs to ask Walensky.
Read 4 tweets

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