Thread by @danielgoyal

❗️Massive…Omicron Disease Severity Study just released in pre-print.

Huge thanks to our South African Colleagues who must have worked through the night to complete this so soon.

Some thoughts on it…
[summary last two tweets]

A good study.
✅ Only reported on cases that had an outcome
✅ Controlled for age, co-morbidity, etc…
✅ Used quite solid proxy for Omicron

✅ admitted limitations -
❌low numbers,
❌no raw data on morbidity or mortality

The most important limitation the investigators highlighted, was the likely difference in vaccine/immune status. Around 50% of the target adult population had at least one vaccine by the time Omicron hit. It was less than half of this at the start of October.

Results
1. Once admitted to hospital, they found no difference in disease severity between Omicron and non-Omicron (mostly Delta) Covid cases.
[for period Oct to end Nov 2021]

This is important for two reasons:
1. They are not simply admitting milder cases, or detecting more incidental cases
2. Admissions can now serve as a reasonably reliable measure for severity.

2. Admission rate for Omicron in South Africa was 2.5%.

For context, our current admission rate in the UK for Delta is about 1.5%.

3. There was a significant reduction in the rate of admissions between the non-Omicron cases and Omicron cases from October ‘21 to end Nov ‘21.
From around 13% admission rate to the 2.5%.

[The authors consider this most likely due to vaccine/immunity.]

4. Expanding the timescale out (v. low vaccine coverage) they included confirmed Delta cases.

Disease severity of admissions was significantly greater in Delta than Omicron.

Doesn’t add much to severity argument, but reminds us that overwhelmed countries do badly!!!

4. Kids
Higher admission rates, but (from small numbers) no clear signal for increased severity.

5. Disappointingly, no specific data was published for death or HDU/ICU requirement. Instead these were all classed as “severe” (prob due to time pressures).

My summary,
Omicron seems to cause significantly less severe disease than recent waves in South Africa, but not less severe disease than Delta is currently in the UK.

And, almost certainly, vaccines seem to remain remarkably protective over severe disease.

[UK decoupling]

Results remain tentative due to numbers and early phase of wave….but we can say:

Good news = vaccines work.
No news = Unmitigated Covid-19 will cause problems.

medrxiv.org/content/10.110…