How Come We Haven’t Reached Herd Immunity Yet?

Via Twitter:

He’s citing the New York Times’ tracker on Americans’ vaccination status, which can be found here. As of Friday September 10, this is where we stood:

65% of American adults are vaccinated. 54% of Americans in total.

If this were a normal vaccine (i.e. one that actually worked) it would mean the virus should only be spreading among the remaining 46% of unvaccinated Americans.

But in practice, viruses don’t work that way. After all, while the government and a number of Vaccine Fanatics on social media would like for us to live in a bifurcated society of vaxed and unvaxed and basically turn the unvaxed into Lepers, the reality is that they mix among one another regularly. Which should make it even harder for the virus to spread, in theory: more immunity, whether via vaccines or natural immunity, among the general population by definition decreases the r0 (i.e. contagiousness) of a given virus.

Say I have Covid and I walk into a large conference room full of 100 people. I strike up a close conversation with one person at random, which means that my odds of spreading Covid to that person are 46% given that the person was selected at random in a room where 54 out of the 100 people are immune. I then start feeling sick, leave the room and go home to lie down without talking to anyone else. If the person I had a conversation with is one of the 54 people in the room with immunity, then my Covid does not spread to that person, and I have not spread Covid to anyone.

If the person I spoke with is one of the 46 without immunity, then I have probably spread Covid to that person. That person in turn probably spread Covid to about 3 other people given the median Covid r0 of 2.8.

This is how the idea of herd immunity works, at least in theory and in a very simplified sense. You want the number of immune individuals–through a combination of natural immunity and vaccine immunity–as high as possible in order to minimize the chances of a virus spreading among the population.

The NY Times says that 90% is the number we need as a country to reach herd immunity, and projects that at the current pace of vaccinations, we will not reach that 90% threshold until June 2022:

But even if the pace of vaccination has slowed considerably since April, when it was at its highest, we still shouldn’t see spiking Covid cases like this:

Granted, this current wave (which appears to have peaked) wasn’t as bad as the wave we saw during the winter given the number of vaccinations plus the number of people who have already had the virus. But it was still a lot worse than it should’ve been in a nation with well over 50% immunity.

And that’s why people are starting to point out that the vaccines don’t work. So what’s the explanation? Delta variant, of course, say the vaccine fanatics:

The vaccine is failing because of VARIANTS, you stupid anti-Science™ idiots!

Which is why we…. need more people to get the vaccine?

This is the one thing I’ve never understood about these vaccine fanatics: their excuse for why the vaccine hasn’t stopped Covid is the Delta Variant. Yet they still insist everyone should get vaccinated, even though by their own admission the vaccine can’t protect you from the Delta Variant.

You can’t have it both ways: either the virus is still spreading because not enough people have gotten the vaccine, or the Delta variant has rendered the vaccine almost useless.

It can’t be both.

Anyway, back to Deace’s original point: why haven’t we reached herd immunity yet despite all the people that have either vaccine or natural immunity? The obvious explanation is that the vaccine doesn’t work, and so when you see a number like 65% of adults being fully vaccinated, that doesn’t actually mean 65% of adults are immune. Vaccinated doesn’t equal immune. Israel says the Pfizer shot is only 39% effective, while the US maintains it’s about 66%.

And it’s failing more by the day. This chart from Handwaving Freakoutery on Twitter projects the rate at which the vaccine is failing, and basically by the time 250 days have passed from a person’s second dose, the vaccine is completely useless:

Within just 90 days, the Pfizer vaccine’s effectiveness falls by about 25%. Within 6 months, it’s under 50% effective.

So we’re not going to achieve herd immunity through vaccination. I know they’re talking about booster shots, but a lot of people who have had two doses of the vaccine are at the point now where they won’t even get the booster shot because of how transparently ineffective their initial shots were. The booster shot is not going to work.

I’ve been saying for over a year that herd immunity via natural immunity will happen around the 20-25% range, and that’s based on looking at when prior flu pandemics throughout history (e.g. Swine Flu, 1957 flu pandemic, Spanish Flu, etc.) peaked out. We’re barely over 10% in the US right now. 41.8 million cases in a nation of about 330 million = 12.6%. It’s probably higher than that due to the fact that there are a lot of asymptomatic and unreported cases. How much higher? Impossible to say, but if we say it’s 50% higher than the actual tested number, then we’re still only at around 18-19%.

And globally, we’re even further from herd immunity: 225 million cases of Covid against a total world population of about 7.8 billion means we’re barely at 3% overall. However, that’s probably significantly under-shooting the actual number of worldwide Covid cases given that testing rates per capita vary wildly from nation to nation. For example, Nigeria is a nation of 212 million people, ranking #7 worldwide. They’re testing for Covid at about 13,500 people per million.

On the other hand, the UK, a nation of 68 million, has conducted more than 4x as many Covid tests as there are people in the country. America, too: we’ve conducted 606 million Covid tests, nearly double the population of the whole country. That doesn’t mean every person has been tested multiple times, it more likely means some people have been tested repeatedly. I know, for example, a friend of mine has to get tested multiple times per week for his job.

The point is, nations around the world vary significantly in their rate of testing for Covid. Brazil, the 6th most populous nation in the world with 214 million people, has only carried out about 57 million Covid tests, which means the US has done more than 10x as many Covid tests as Brazil has. Official global numbers for Covid are likely to be an extreme low-ball scenario.

So this is why I predominantly focus on the US. It’s a whole different can of worms to try to figure out the real number of people worldwide that have had Covid.

There is actually a formula used to calculate the herd immunity threshold, and it’s based on the r0 of a given virus. It’s as follows:

1 – 1 / r0

So that would give us a herd immunity threshold of about 64%, but then again, the more people that get infected and recover (and thus gain natural immunity), the r0 of the virus decreases. Fewer people to infect obviously means fewer people infected.

Also, the Delta Variant’s r0 is estimated to be about 6, which further complicates things. That would put us at a herd immunity threshold of ~83%. Comparatively, the Spanish Flu had an r0 of about 1.8, which is lower than even normal Covid and way lower obviously than Delta.

So the bottom line is that we haven’t reached herd immunity for two main reasons:

  1. Not enough people have natural immunity yet.
  2. The vaccine is failing.

The vaccine was supposed to be a substitute for natural immunity, which would help us get to herd immunity way faster than natural immunity would. It’s like this: if we have 12% of the country naturally immune, and the herd immunity threshold is, say, 70%, then we have can fill that 58% gap by vaccinating people and boom, 70%.

But again, that’s assuming a 100% effective vaccine. And this vaccine is nowhere close to 100%.

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