Clear explainer of a very carefully nuanced report. While the main thing to say is "small numbers," it does seem that the average severity among those in the hospital is comparatively low. Two thoughts about interpretation:
1/ Omicron growing very fast. Patients hospitalized for COVID are typically (not always) well into their infection. In a fast-growing epidemic, the proportion infected 10d ago, say, is lower on any given day than in a slow-growing one. This alone could cause unusually lo ...
proportion of hospitalizations with primary diagnosis. Fast-growing epidemic = most infections are new is basic demographic theory (just like in a fast-growing population of people, most people are young). The unusually high growth rate can at least partly explain observation.
2/ Commentators note that the population in hospital with SARS-CoV-2 is younger than in the past, and that vaccination is highest in the older ages. This could be evidence that it's milder, as @AmeshAA notes or that vaccines are protective as @MarionKoopmans notes, but...
.. hard to take it as evidence of both. If the older population is protected by vaccine, it would leave only the younger, in whom even earlier variants were comparatively mild. Either vax protection against severe disease, or lower severity in all would be good news.
But if one infers either from the data then there's not much left to support the other. Overall, this is certainly better news than we might have expected with exploding case rates, but apportioning between growth rate, vaccine effect, and lower severity will take more research.
Kudos to @MRCza for getting these important early data out

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More from @mlipsitch

18 Aug
@CT_Bergstrom @jsm2334 Certainly this kind of bias merits consideration. I think the particular figure cited in that table is an example of Simpson's paradox, which is a special type of confounding.
@CT_Bergstrom @jsm2334 For those new to these terms, confounding is just the problem that (in this case) vaccine is not randomly distributed in the population, so the vaccinated have different risks from the unvaccinated for reasons other than their vaccine: in this case, age.
@CT_Bergstrom @jsm2334 Simpson's paradox is an extreme form of confounding in which a combined analysis for two groups of people gives an unusually misleading estimate, relative to the (more) accurate estimate for each group individually.
Read 17 tweets
13 Aug
As often happens, the headline is too simple for the more subtle message of the article…
The article's main point is unarguable: "we cannot control the delta variant by maximizing the immunity of only a segment of the population."
But some (incl me) have thought the main goal of vaccination all along should be to defang (make less harmful) not defeat (eliminate) the virus.
Read 7 tweets
20 Jul
At the risk of boiling down too much and certainly losing some detail, one way to summarize this wonderful thread is that when we think about vaccine effectiveness, we should think of 4 key variables: 1 which vaccine, 2 age of the person, 3 how long after vax, 4 vs what outcome.
We've been using the simple view that the major vaccines in use in the US/Europe are possibly less effective against infection/symptoms when a variant is involved, but remain highly effective against severe outcomes. Published data so far support this view.
To be more precise, we would say "so far in the general population, up to about 6 months after vaccination, the vaccines have held up against severe outcomes even from Delta, though there is some evidence from Israel, UK, and Canada of declines in effectiveness vs infection."
Read 14 tweets
7 Jul
Different approach from many other VE studies, following HCW vaccinated vs unvaccinated, tested when exposed to a case, to assess VE against infection given exposure, consistent with our recommendations in…
Also looked at infectiousness (proxied by Ct). Take home messages: fully vaccinated 65% (45-79) protected against infection given exposure. This is lower than other estimates of symptomatic or arbitrary mix of symptomatic and other cases, as expected.
Read 8 tweets
13 Jun
Now out with @rebeccajk13 Interpreting vaccine efficacy trial results for infection and transmission…
funded in part by #SeroNet
In which we show that earlier work by Rinta-Kokko et al on interpreting prevalence measures for vaccine efficacy generalizes to the COVID-19 case and that the odds ratio for PCR+ in vax vs unvax persons swabbed at random
is under reasonable assumptions a lower bound on the vaccine's effect against transmission, the critical quantity for herd immunity that combines reduced risk of acquiring and shorter duration.
Read 11 tweets
25 May…. A key point: lab leak does not imply manipulation and manipulation does not imply ill intent.
I disagree with @SenTomCotton on many many things but this set of tweets quoted in the article lays it out correctly
In contrast this statement is illogical “However, since we observed all notable SARS-CoV-2 features, including the optimized RBD and polybasic cleavage site, in related coronaviruses in nature, we do not believe that any type of laboratory-based scenario is plausible.”
Read 4 tweets

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