You all know the data demonstrating dramatically higher hospitalization rates for unvaccinated folks

But one key point often not discussed?

Around 60%-70% of unvaccinated adults have already been previously infected

Which tells us a lot about infection-induced immunity

We see large gaps in hospitalizations between vaccinated and unvaccinated

But unvaccinated are not immunologically naïve

At this point, probably 2/3 have been previously infected

And yet, we still see 50X differences in hospitalizations between vaccinated and unvaccinated

One possibility is that hospitalizations are happening in the dwindling group of unvaccinated who haven't been previously infected

Means true benefit of the vaccines is even higher (by a lot)

But much more likely, it means infection-induced immunity is not holding up

My best estimate is that 3 months after an infection, certainly 6 months after infection

Immunity from infection starts to break down

Which is why we are seeing a lot of unvaccinated people get reinfected, sick, and end up in the hospital

But let's do the counterfactual

Imagine that infection-induced immunity was AS GOOD as vaccines

What would we see?

Early, when unvaccinated were largely immunologically naïve (i.e. not previously infected)

We'd see a large gap in population-level hospitalization rates between vaxxed and unvaxxed

Over time, as more unvaccinated people got infected,

If infection-induced immunity was great

We'd expect gaps in population-level hospitalization start to close

Because unvaccinated would increasingly be made up of previously-infected folks (as they are now at 60-70%)

So is that what we see? A closing of the gap over time?

In fact, the opposite

Obviously, a lot of other stuff also going on, including which variants are dominant, etc.

During each moment in the pandemic, it is better to be vaccinated

And over time, the gap is widening

Now fans of infection induced immunity might argue that these folks just aren't getting reinfected

So as proportion of unvaccinated folks with infection-induced immunity rises

You should see a fall in infection rates among unvaccinated people

We see the opposite

So let's be clear about a few things

Is infection-induced immunity real?


Does it help prevent future infections/hospitalizations?

Probably...for a while

For first 90 days or so? Almost surely

Beyond that? probably not that much

Infection-induced immunity is helpful

But really doesn't seem to last that long

And as virus becomes endemic

You are looking at constant reinfections

Or you could just get vaccinated

And avoid all the heartache and misery of having to get infected over and over again


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More from @ashishkjha

Feb 1
I've been saying for weeks that as cases recede

We can soon relax public health restrictions

I think of this like the weather

When it is bucketing rain

Umbrella, rain coat, boots, are all essential

When the storm turns into a drizzle, those become less critical

A big spike (like Omicron surge) is like a major storm

If you don't want to get wet, you need to stay home

But if you venture out

Bring a big umbrella (vaccines)
Wear a raincoat (good masks)
And rainboots (avoid crowded indoor spaces)

You get the idea

Right now, the storm is starting to ebb

Infections are falling, hospitalizations down

But with infections still high

Indoor mask mandates make sense. As do indoor capacity limits

Many states still have them (though bars are open in every city in America, as far as I know)

Read 9 tweets
Jan 25
We're in a transition moment in this pandemic

We're coming off highs of the worst surge of infections we've ever had

Cases are high but starting to fall in much of the nation

This moment raises lots of questions

With one big one: What happens next?

As Yogi Berra once said,

It's tough to make predictions, especially about the future

So we should be circumspect about how much we can predict with certainty

But some things seem pretty reasonable to assume

First, infections are likely to decline in upcoming weeks

Here's wastewater data from Massachusetts

Infections are falling fast. Expect to get to pre-Omicron surge levels within a week or two

The rest of the nation will soon follow

And by Mid-February, infections should be relatively low across much of the nation

Why low?

Read 14 tweets
Jan 20
Getting asked when will Omicron peak in the US?

My best guess?

I think we are there

We are seeing a little bumpiness in the data because of MLK day holiday

But evidence says as a nation, we have likely peaked

Big states: CA, FL, and NY have peaked. May be even Texas

Beyond peak, there are two surprises worth discussing

First, I said few days ago that I expected hospitalizations to rise a while longer

Turns out, not so much

Hospitalizations have flattened nationally and are declining in places like NY

Why? What did I get wrong?

The reason my guess on hospitalizations may have been too pessimistic?

In previous surges, cases caused hospitalizations and folks stayed in hospital for a while

With Omicron, fewer hospitalizations

And Omicron hospitalizations are, on average, much shorter

That's good!

Read 7 tweets
Jan 16
Quick update on the pandemic in US

We're averaging about 800K identified cases daily

Likely missing 75% - 80% of infections

If you do the math

At least 1 in 100 Americans getting infected every day

Everyone wants to know: when do we peak?

Here's the national picture

The national picture shows a slowing of the surge

But we're still rising

But if we dig a bit deeper, a few things emerge

First, let's start with the big 4


Why? Lots of people live there, geographically and politically diverse

What do we see?

a few things
There is no doubt NY has peaked, down a lot

FL looks like it has peaked, down some

California may be plateauing, likely

Texas is hard to tell, likely still rising, not sure

And that is the 2nd big point:

There is no single national experience

Local conditions vary, widely
Read 8 tweets
Jan 10
Given the immense value of in person schooling for America's kids,

Lets talk about how every school can be in person safely today

Not under ideal conditions

But under real-world conditions

First, let's start with "ideal", which LOTS of school districts have done

What is ideal?

1. Teachers vaxxed/boosted
2. Kids vaxxed
3. Everyone masked w/good masks
4. Ventilation
5. Testing

Billions of $ available for ventilation and testing
Vaccines free, widely available

I get it, some places chose not to do it

But $ is not the barrier

So lots of school districts chose not to do these things

What if a school doesn't have testing and systemic upgrades in ventilation?

Can schools still be safe?


If folks vaxxed/boosted
And we have masking (compliance doesn't have to be 100%)

Still very safe
Read 7 tweets
Jan 8
Watching national data

And being in the hospital this week

I see two things that appear contradictory

But both are true

1. Link between cases & hospitalizations is much weaker with Omicron than in the past

2. Our healthcare system is in trouble

Thread: the moment we are in
Let's talk about I'm seeing in the hospital first

In the hospital, seeing lots of COVID patients

Some admitted due to COVID

They are all either:

1. Unvaccinated

2. Very high risk folks not boosted

And some admitted "with" COVID as incidental

Almost all not boosted

Haven't seen a single boosted person admitted for COVID

And in the national data

Risk of hospitalizations is still those two groups

High risk not boosted

And that pool of people is still very, very large

And that is driving the surge of hospitalizations

Read 14 tweets

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