Thread by @ashishkjha

As the Omicron surge of infections abates,

Its worth reflecting on few lessons we learned

Today, lets' discuss whether Omicron was indeed "milder"

Short answer? Yes it was

But it still caused a devastating loss of life

And that's a lesson for managing future waves

Thread

First, let's talk about how we might assess whether Omicron was "milder" than Delta

One way is to look at case fatality rate

Remember CFR is proportion of identified cases that end up dying

Throughout the pandemic, the CFR of of COVID in the US has been between 1.5% to 2.0%

CFR is usually 1.5% but rises to 2.0% during surges as hospitals fill

Meaning that as hospitals fill up, admission thresholds rises...and ability to care for sick people diminishes

Its bad to be sick during a COVID surge

So what happened to CFR over the past 2 months?

Remember there's about a 3 week lag between cases and deaths

Omicron cases started taking off around December 20

Before that, it was all Delta

And after mid-January, all Omicron

This lets us look at 3 time periods and calculate CFRs

Delta only
Mix of both
Omicron only

3/n

So what do we see?

During the Delta stage (deaths from infections that happened before 12/20)

CFR was about 1.6% (with a dip due to holidays)

As Omicron took off, we see CFR plummeting

And by the time we get to later January, its all Omicron deaths

And CFR was down to 0.4%

So CFR fell from 1.6% during Delta to 0.4% during Omicron

Lowest CFR we've seen in the pandemic

Means that for average "case", chances of dying fell by 75%

But there's more context

First, we probably missed a lot more Omicron infections because folks testing + at home

4/n

If all those home tests had been reported, CFR would be even lower for Omicron

Why did Omicron infections have such low mortality rate?

1. It infected more vaccinated people than Delta did. Vaxxed folks far less likely to get severe disease

2. Omicron is inherently less severe

One more fact

When Delta was dominant:

An average of 1200 Americans died each day

When Omicron was dominant

An average of 2200 Americans died every day

So this "milder" virus with 75% lower CFR

killed nearly twice as many Americans every day

6/7

So in sum,

CFR for Omicron in the US during surge was 0.4%

About a quarter of what it was for delta

That really is good

But Omicron surge caused so many infections

That it killed about 50K people just in the last 3 weeks

7/8

So here's the lesson:

So even if future variants are less virulent (no guarantee they will be)

A large surge can be deadly

So what do we do?

Before the next surge

Let's get more people vaxxed/boosted

And be ready with smart strategies to prevent runaway infections

End