Omicron Severity

On the question of whether Omicron is relatively mild variant or not the press should be more precise.  I think most people want to know is the virus more severe to a person rather than the societal level of hospitalizations.  for example it’s possible that it similar to delta for those without antibodies but a lot milder for breakthrough and or repeat cases.  I don’t think UK or NYC hospitalization levels support the null hypothesis that delta severity = omicron severity.  But certain charts makes me wonder if maybe if it is as severe as Delta for the unvaxxed/unimmunized.

One epidemiological feature of Omicron is probably a shorter spikier peak.  I'd say at least in NYC we're highly likely to exceed the 400 daily hospitalizations of last Winter (if already 200 per day on Monday).  But in terms of bed capacity we will probably be ok because the admissions spike will last a few weeks instead of being elevated for 3 months.  It may be a different story in the low-vax/low-immunity deep south and plains states.

​And this Pfizer pill is a game changer. Biden bought 10 million pills in advance.   Unfortunately the world has to share 180K pills during 2021.  Even if we got a 100% allocation, this would cover only the 180K people that tested positive Tuesday.  I think that if they give the pill out like they do the monoclonal antibodies, maybe only 1 in 50 will 'need' it, but they have to give it to 1 in 5 to make sure they capture that 1 in 50.  Very curious how they are going to distribute the pills - do they do it like they did vaccines where they leave it up to the states?  Do they let the PBMs and pharmacies figure it out?  Go straight to the hospitals?  Will they give the pills until they run out like vaccines or ration them for only the unvaxxed/immunocompromised?  Will a state decide to deny them to those without a vax card or good excuse?

The Scotland study that dropped yesterday seems to me the best (by far) study out there about Omicron severity.    In Scotland they have a vaccine database and they were able to link the database it to a database that "variant-types" ~150K COVID cases in November, about evenly split between Delta and Omicron.They took the Delta infections as a given to regress the odds of hospitalization based on age, sex, poverty, Covid test history, and comorbidities.  They included vax status based on type of vaccine, doses, duration, and a calendar period effect they found.   They took this regression model and applied it to Omicron cases to predict hospitalizations.  The hospitalizations, unlike the England study, were admitted patients (as opposed to people who showed up in the ER).  Really perfect study design in my opinion.Here's the output. S Gene Negative means Omicron, and S Gene Positive means Delta.  Because they were typing 140K cases I think they had to use this less precise test so they have some gray areas between Delta and Omicron. Regardless you can see that omicron hospitalizations were at only 32% of expected.  They fixed the flaws in some of the other studies that show a 2/3 reduction because they were comparing two different time periods (South Africa), ignoring age (Denmark), or including ER visits (England).    My only quibble here is that i don't think they did multi-factor interactions in the regression and Scotland has a 0% vaccine rate for the kids so it might distort the true unvaccinated picture here.  Kids have a lesser market share of Omicron than Delta and a naturally lower hospitalization risk.Very few places on Earth would be able to assemble this data. God save the NHS.

​Scotland doesnt address length of stay but they have the data so I expect they will soon.  South Africa had dramatic length of stay reduction which some chalked up to mild cases in kids.  England did a study but not helpful because they include the self-selecting ER cases, so the avg length of stay is measured in hours rather than days.

We dont know how Omicron immunity will last, or if it will protect against other variants.  Like for example we could see a Summer surge of Delta if Omicron doesnt provide immunity against it.  We have a good idea that the earliest vanilla COVID has immunity that can be modeled in a population sort of well as a straight line from 3 months to 16 months (like 100% are immune for first 3 months, at 9.5% 50% are immune, 0% at 16 months).  If Omicron follows this pattern great. If it protects against past and future variants we likely have herd immunity.

Hard to test because after the first person with Omicron has recovered, Delta is somewhat displaced.There was a cool study in South Africa where they took the Omicron infected plasma and then the two-weeks-post-Omicron plasma of 13 people vaxxed and unvaxxed people to the lab and introduced both Omicron and Delta.  They found that Omicron exposure increased the neutralisation 4.4x after you beat Omicron compared to when they introduced Delta to the newly tested Omicron.  IIRC this kind of test measures the 'titers' created in the blood plasma.   For context when they did the same thing but introduced Omicron there was a 14x increase in titers. And from memory when Pfizer/Moderna introduce vaccines/boosters and do a similar test to healthy individuals the increase is in the dozens, like 30x or 40x.At a high level I think that on day 1:Vax against delta > vax against omicron > omicron immunity against omicron > omicron immunity against delta.And the wrinkle here is that the vax against omicron seems to deteriorate faster than the vax against delta, and both of those decrease faster than COVID natural delta immunity.  And we have no tests of speed of decay of COVID natural omicron immunity