Thread by @MatthewDavidH

Tragic as it is, the current US wave of COVID-19 cases, brought about by the combination of insufficient vaccination, premature openings, & more infectious Delta variant, would be far worse had we not vaccinated a substantial proportion of our population. Especially OLDER people.

As @_stah & @jonahfleish were among the first to notice (others are starting to notice it now), while US cases and hospitalizations are still rising, it looks like hospitalizations may peak before cases.
IF THIS HAPPENS, it will be good news among the ongoing tragedy.

To understand why the relative timing of cases vs hospitalization peaks is a REALLY BIG DEAL right now, you need to think about age-specific mortality and vaccination rates.

Because older people are at so much higher risk of hospitalizations and deaths when they get infected, vaccinations began with the oldest people.
And since most older people knew they were at higher risk, fewer of them hesitated to get the shots.

For many months I have been doing a simple but important calculation: multiplying the percentage of prior US deaths in each age bracket times the percentage vaccinated (full and partial) times plausible estimates of vaccine effectiveness.

I lowered my effectiveness estimate for Delta, but only slightly because for deaths these vaccines remain extremely effective vs Delta. Delta PARTLY evades Delta, which greatly reduces effectiveness against infections, significantly reduces effectiveness against hospitalizations

but only slightly reduces effectiveness against deaths.

Anyway, without going into all the numbers, my conclusion has been that current US vaccination coverage reduces Infection Fatality Rate of Delta by roughly two-thirds from what it would be without any vaccines.

The reduction in Hospitalizations Per Infection from vaccination in the US is less dramatic than the reduction in Deaths Per Infection.

There is tremendous variation among US States for vaccination coverage.

There is also tremendous variation among US States for percentage of the population who have been infected before the current wave, and therefore have some immunity from prior infection.

Experts disagree on whether infection with a previous variant of the virus, or vaccination with an mRNA sequence designed for a previous variant of the virus, gives greater protection against Delta.

They ALL agree that EITHER source of immunity gives HUGE protection from death.

They ALL agree that getting vaccinated first is MUCH SAFER than getting infected first.

They ALL agree that once you have immunity, however acquired, IF you get what the media calls a "breakthrough infection" (a term I do not like; I prefer to say just first or second exposure),

then after you have had BOTH vaccination and infection, or BOTH infection with prior variant and infection with Delta, after two different exposures you'll probably end up with super-duper immunity.

So if you got vaccinated, and you get a mild case of COVID-19 now, that does NOT MEAN THE VACCINE FAILED. You almost certainly would have had a much worse case had you not been vaccinated first. And once you recover, you'll probably have super-duper immunity.

I have been fully vaccinated. Delta is so infectious that I will almost certainly get infected sooner or later, as will nearly everybody on the planet. Since infection is probably inevitable, and probably won't make me seriously ill when it happens, why do I wear KF94 masks?

I wear KF94 masks now because DELAYING my inevitable Delta infection is an excellent idea right now!

1. If I am unlucky and need hospitalization, I'd rather be hospitalized AFTER the pandemic has subsided.

2. I might get a booster shot before I get infected.

3. I'd rather not infect the older people around me before they get their booster shots, if booster shots turn out to be needed!

So, having summarized what we know about the immunity from vaccines or prior infections, why is the relative timing of hospitalization vs infection peaks such a big deal?

Because IF hospitalizations peak before infections, that will mean this wave is being ended mainly by immunity.

Previous waves in the US always ended from a combination of weather and people changing their behavior. Most people do not seem to heed warnings from scientists.

But people DO start changing their behavior when chaos at local hospitals dominates TV news. So the typical pattern has been that infections keep rising until enough people get scared by what they see on the news or hear from friends and relatives about local hospitals.

Since there is a lag time between infections and hospitalizations, when infections are brought under control mainly from behavioral changes that means hospitalizations continue climbing for some weeks after infections have ceased climbing.

Thus, in all previous waves, hospitalizations peaked AFTER infections peaked.

IF we see hospitalizations peak before infections this time, that means something different has happened.

Specifically, the dynamic that I and others have been expecting for a while may finally have begun to occur: the virus may be running out of immune-naïve older people.

This dynamic, the virus running out of immune-naïve OLDER people before it runs out of immune-naïve YOUNGER people, is probably why the UK saw decoupling of hospitalizations and deaths from cases before the US has: the UK did a better job of vaccinating its older people.

Over the next few weeks, we will get data telling us whether or not this wave is ended mainly by immunity or mainly by people changing their behaviors.

Because until immunity becomes the main thing slowing down infections, containment of the pandemic is very fragile and it can explode again once people relax precautions again.

Once we have reached the point where most people have been exposed to this virus, it will not stop evolving just as the 1918 pandemic Influenza virus never went away.

Here is an excellent interview with one of the world's top experts on what the longer-term future might look like:
theguardian.com/world/2021/aug…

Now, having laid out the big picture as I see it right now, let's drill down on some individual States.

You might want to print out hardcopies of these graphs to follow along!

I think every State is going to end up with a high level of immunity one way or another.

Some States, such as VT, HI, & ME, did a good job both containing the virus and getting people vaccinated. They are at high levels of immunity now, and got there mainly by vaccines.

South Dakota also has a high level of population immunity now, but they got their immunity mainly from infections. SD has had more than five times as many deaths per capita so far as VT has had.

Most US States are somewhere in between VT and SD. Where VT will end up immune mainly from shots, and SD will end up immune mainly from infections, the US as a whole will probably end up immune from a mixture of the two.

Sadly, many countries around the world still cannot get many doses of vaccines, and will therefore probably get most of their immunity to the SARS-CoV2 virus by infections. With tragic consequences.

By now COVID-19 has almost certainly killed something like 10M or 20M people.

Most of those deaths will be in countries where they do not have good statistics, so we shall never know the true death toll from this pandemic.

But we must learn from it, and prepare for the next pandemic, so that we will be able to respond more effectively.

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