Lots of chatter about how early data show #Omicron is "less dangerous". But it is important to correct for the lag between infection and hospitalization when comparing the severity of variants with very different properties when it comes to transmission, here’s why 1/n
Imagine two viruses exactly the same in terms of severity, but one of them infects on average 3 people, and the other 1.1 (I know you can’t have 0.1 of a person, it’s an average). These are the effective reproductive numbers or Re and they determine how quickly they spread 2/n
If we start with 1000 infections with the less transmissible variant and just one of the more, we would expect the latter to overtake the former by the 7th generation (assuming nothing changes). Exponentials are wild 3/n
(yes those are both exponentials, it's just the exponent in one is smaller than the other and that makes a big difference) 4/n
Now assume the sickest people only get hospitalized 4 generations after they are infected. Almost all the hospitalizations we we see are with the less transmissible variant. The hospitalizations from the more transmissible have not yet started to increase rapidly 5/n
This is not only an issue at the start of the exponential but for anything growing at a faster rate. because new cases enter the denominator faster than the ones that subsequently turn bad are counted in the numerator 6/n
To account for this when comparing variants you have to account for different growth rates *and* the lag time to severe illness (thx @baym for emphasizing this). Of course the lag time might change adding another complication 7/n
And many other complicated things can go on. For now, remember that we are seeing the hospitalizations that resulted from infections that started about 2 weeks ago. And that was only a few days after Omicron was described and before it was reported in many places 8/n
The rate of increase may slow a bit because people, especially vulnerable people, alter their behavior. I also want to emphasize we don’t have a good handle on severity in highly vaccinated populations. But a lot of people in many parts of the US remain unvaccinated 9/end
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#Omicron data continue to accumulate, with this being perhaps the most serious indication I have yet seen about what we should expect in the next few months. Like @theosanderson says, these are increases in *daily* results 1/n
Was distracted before continuing the thread, and in that time this dropped. Once again the @UKHSA has provided incredibly prompt data collection and analysis. The upshot is that #omicron is definitely transmitting very readily indeed, and that matters 2/n assets.publishing.service.gov.uk/government/upl…
Even if Omicron infections are mild (and they might be, especially in vaccinated people) they would have to be really really mild to prevent an acute burden on healthcare that is already stretched, resulting from very large numbers in a short period of time that will add up 3/n
There is a lot of anger in the UK about this. More to the point it is an unambiguous and appalling failure to take the pandemic seriously at one of its most damaging inflexion points. It has come to light at another such moment as Omicron surges 1/n itv.com/news/2021-12-0…
Look at the date of the video: 12/22. In other words the week *after* Matt Hancock announced the existence of B.1.1.7/Alpha in the House of Commons and warned how serious it was. The partygoers cannot pretend to have been unaware 2/n newscientist.com/article/226307…
And look at the consequences of such behavior, the spike in Alpha transmission that was the result 3/n
This is a little astonishing to see. Rapid tests are a part of the pandemic toolkit and should be readily available to everyone (*not* after any baroque claim on insurance). Things are, as ever, a little more complicated 1/n
For a start, Rapid Tests alone do not keep case counts low (even if they might be lower than they would be in their absence). Look at the UK where rapid tests have been handed out free for months. Those are not smoothly controlled epidemic curves 2/n
There are situations like this, where rapid tests shine 3/n
Given how serious Omicron could easily be, some people might be breathing a sigh of relief if the worst possibilities are ruled out (I think they will be). But that still leaves a lot of possibilities most of which are Really Not Good. However this is not a thread about that 1/n
Pandemic twitter often tries to divide people into ‘pessimist’ or ‘optimist’ camps. This is not helpful. Especially when it comes to the folks who know most about infectious disease. I am neither an optimist nor a pessimist. I am a scientist and I try to call it like I see it 2/n
I’m not always right, but I am sincere and I try to correct when I am wrong. And I admire people who do the same. I don't always agree with them all, all the time. But that comes with the territory 3/n
A little over a week since it was announced it is already clear that Omicron is really serious. Some important pieces of evidence have begun to coalesce. While the worst outcomes still seem unlikely, what we have is quite bad enough to be going on with, a thread, with nuance 1/n
First the spatial spread. Recall previous variants and the pace with which they were reported in different locations. Omicron is already on all continents other than Antarctica in slightly over a week since it got named. I mean... wow 2/n
Meanwhile we get some relatively positive news in that hospitalized cases seem milder than in previous waves. The concern is that those infected and hospitalized so far are mostly young. And we would expect younger folks to have milder infections statnews.com/2021/12/04/omi… 3/n
With #Omicron very real, I thought it worth going back to this, which I wrote with @mlipsitch at the start of the pandemic. It helps to think clearly about 3 types of information we have at the start of an outbreak amid uncertainty 1/n blogs.scientificamerican.com/observations/h…
First there are the facts, then there is the interpretation of those and what they might mean about things that we’ve not been able to yet nail down into facts. This means expert opinion, based on previous experience, unpublished data, and conversations with colleagues 2/n
Then there's speculation. Sure it can be useful. But without a way to test whether we should take it seriously, we shouldn’t. Note that this can include really important things like why a particular policy choice was favored, but that’s not science 3/n