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by tunesmith 1722 days ago
You can walk yourself through the reasons why with simple math, really.

Every disease has an estimated R0. The number of people an infected person will infect. You probably have heard of this.

Delta, last I checked, has an estimated R0 of between 5 and 9.5.

Vaccination levels reduce that. And it's a simple equation. All you need to know is the vaccination rate for your population, and an estimated efficacy rate of the vaccine.

And from that, you can figure the new adjusted Rt:

rt = r0 * (1 - (vacRate * eff))

And that's it. And no matter what efficacy rate you pick (infection efficacy estimates for mRNA against Delta vary widely), the resultant rt will be less than the initial r0.

And if it's less, then that effectively means that the disease is less contagious for that population, compared to how contagious it was pre-vaccination.

And less contagious is better than more contagious.

So now I am legitimately curious. What part of the above reasoning do you actually disagree with?

(Incidentally, vaccination also improves your chances of avoiding future infection, even if you've already been infected.)

6 comments

What is the efficiency against transmission of the latest mutations? AFAIK there is a great efficiency against bad symptoms, but much lower efficiency against transmitting the disease to others, but I don't know the latest numbers.
(Copied from elsewhere in the thread:)

Last I heard, the CDC gave a 95% CI of the mRNA vaccines being 26% - 84% against infection (from Delta), and there's an additional 40% - 60% protection against infecting others (I've seen that estimate in multiple places but I don't know the source). If that's true, it suggests an overall range of 55.6 - 93.6 effectiveness against infecting others.

Over the summer Florida has been in the news because of an ongoing epidemic spike. Using hospitalization rates, the spike started sometime in early July. By late Sept it is almost gone. The fully vaccinated rate increased from 48% to 59% during the same time period. Is the receding fully explainable by the increase in vaccination rate, or can we consider other forces at play, for example forces of outside human control that have been at play in every single epidemic before the vaccines era?

https://coronavirus.jhu.edu/region/us/florida

https://data.democratandchronicle.com/covid-19-vaccine-track...

Edit: I plotted Rt as a function of eff, assuming r0=7 and vacRate=1. Rt goes below 1 only for values of eff > 0.85, which means that given the numbers for eff you gave in a different post "overall range of 55.6 - 93.6 effectiveness against infecting others", there are plenty of scenarios where vaccines by themselves cannot stop an infection wave even if the population is 100% vaccinated.

https://www.wolframalpha.com/input/?i=plot+y+%3D+7+*+%281+-+...

https://www.wolframalpha.com/input/?i=solve+1+%3D+7+*+%281+-...

Edit2. For a 0.59 vacRate, there are some solutions for R0 * (1 - 0.59 * eff) < 1 with eff in [0, 1] and R0 in [0, 9], specifically there are solutions for R0 < 2.x Not going to cut it for 0.59 vaxx rate and delta, no matter how effective the vaccines are.

https://www.wolframalpha.com/input/?i=plot+1+%3E+y+*+%281+-+...

Some combination of death, natural immunity, vaccination, distancing, mask use, etc. What other forces are you suggesting?

Note that the more populous counties probably increased vaccination at a greater rate, like Miami-Dade went from 56% to 72% over the same time range.

Natural immunity as a direct effect of an infection wave is my first guess. In some circles 'natural immunity' has become a dirty word :/

The assumptions between the equation rt = r0 * (1 - (vacRate * eff)) are too simplistic and unable to explain Florida infection wave behavior. There are more variables that we ignore when focusing only on Rt and vaccines.

The silver lining: At some point the whole population would have been exposed to covid, either through vaccines, infection or both. At that point the whole vaccination rate / effectiveness discussion becomes moot. Perhaps I wish the public discourse would keep an eye on 'estimated population fraction exposed to covid' that includes all plausible factors.

Yes, I brought up that equation merely to illustrate how vaccination alone can impact Rt downward - for a while it was unclear to me exactly how "partial vaccination" (before herd immunity) was a benefit; that helped me see that it really just mean it slows down the doubling rate until you get to Rt=1. But overall, Rt is impacted by all forms of mitigation including natural immunity.

The way I actually use that equation in my personal dashboards is to estimate what Rt "would" be, at today's mitigation levels, if no one had gotten vaccinated. So for instance, Portland's Rt is currently 0.92 (according to one model). By plugging in Portland's vaccination rate and efficacy estimates, you can estimate that Portland's Rt would be around 2 today if not for the vaccinations, if all other mitigation were the same.

On the one hand, 2 is a lot better than those estimates of 5 to 9.5, which means that we're impacted a lot by current mitigation practices (masks, distancing) and natural immunity. On the other hand, 2 is huge! Given estimates on infectious periods, that means that currently our cases halve every 90 days or so, but 2 would mean cases would be doubling every week or so. Gargantuan difference. So just an illustration that vaccination has a big impact and matters a lot.

or maybe they're just reporting data creatively

https://www.reddit.com/r/dataisbeautiful/comments/pxizb1/oc_...

and it seems like it works

This is missing the last step of calculations as any degree of lower r0 doesn’t necessarily prevent endemic disease. My understanding is that at this point, vaccines are about keeping symptoms mild and ICUs at low capacity through reduced spread and more effective immune responses. This seems compatible with the view that we will have to live with this disease for a long time.
you argumentation is correct but misses a point. the vaccs may encourage new variants due to evolutionary pressure.
That point is incorrect; discussed elsewhere.
I mostly agree with you but "And less contagious is better than more contagious." is a giant hand wave in a logical argument. You should explain what specific outcome in the longer term improved by this and justify that.
The implicit assumption in that statement is that "less contagious" means "less disease" means "less casualty".
Other ideas https://boriquagato.substack.com/p/the-vaccinated-supersprea...

It is all much more opaque than the "get your vacc and your old live comes back" evangelists want you too believe. Corona will stay.

I don't know what pro-vax people are saying "get vaccinated and your old life comes back", that seems a mischaracterization to me. The reason to get vaccinated is to protect yourself and others from the disease.
Once everyone (young kid less than 5 years old) can get the vaccine if they want to, I really doubt Covid restriction will stay in place.