Thread by @ashishkjha

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

Thread

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

2/7

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

3/8

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

4/5

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

5/9

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%)

6/8

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

7/9

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

8/10

So let's be clear about a few things

Is infection-induced immunity real?

Absolutely

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

9/10

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

Fin