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Will COVID be eliminated once everyone is vaccinated?


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Once everyone has been vaccinated, is it to be expected that COVID will simply die off in lieu of any further hosts or will it be forever bouncing around like the flu, opportunistically infecting the odd unvaccinated person or the 5% of the vaccinated (as the vaccines are supposed to be 95% effective) whose defenses it manages to get past?

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1 minute ago, Alfred001 said:

Once everyone has been vaccinated, is it to be expected that COVID will simply die off in lieu of any further hosts or will it be forever bouncing around like the flu, opportunistically infecting the odd unvaccinated person or the 5% of the vaccinated (as the vaccines are supposed to be 95% effective) whose defenses it manages to get past?

In time, possibly. Smallpox for example has been eradicated...Polio also I think. 

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52 minutes ago, Alfred001 said:

Once everyone has been vaccinated, is it to be expected that COVID will simply die off in lieu of any further hosts or will it be forever bouncing around like the flu, opportunistically infecting the odd unvaccinated person or the 5% of the vaccinated (as the vaccines are supposed to be 95% effective) whose defenses it manages to get past?

Could be the latter if the rate of generation of new variants exceeds the ability of vaccines to keep up. We are years from vaccinating the whole population.

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Polio is still endemic in Afghanistand and Pakistan and I believe there have been irregular detections elsewhere.

To OP, at this point it is not clear. If vaccination was available early in the pandemic and/or if the infection levels where kept at a low level until now, and if everyone was getting vaccinated, then the answer would have been a yes.

However, one should take a step back in understanding how eradication works. It is not necessarily just a matter of vaccination, but it is about creating a situation where an infected person is unable to infect enough folks to sustain pathogen spread.

Herd immunity could be achieved by a combination of vaccination, immunity, as well as social measures (e.g. distancing) for example. 

But right now we have still over 14.8 million detected infections (and likely many more undetected) which is a huge reservoir for the virus and has a high risk of the creation of new variants. I have lost track of how many variants there are now in circulation, though only relatively few are classified to be of concern. Nonetheless, there is a big risk that for at least some of the variants, the vaccine will be less effective. We have already observed across the world that the UK variant (B.1.1.7) has displaced the wildtype. And this also affects how we should interpret vaccine efficacy data. Pfizer/BioNTech and Moderna efficacy data were generated earlier in the pandemic where mostly the wildtype was around. However, AstraZeneca already included data from patients with the B.1.351 (South African) strain, against which the vaccines might not work as well.

Some smaller data sets indicate for example that the Pfizer/BioNTech vaccine is about 89.5% effective against any infection with the B.1.1.7 variant and only 75% against B.1.351 in some groups (DOI: 10.1056/NEJMc2104974). However, they still protected with over 90% against severe diseases. The issue there is that while it prevents hospitalizations, it is still possible that folks get infected and may potentially transmit it to vulnerable persons.

Aside from variants we got the issue that in many (most) populations we will not achieve anything close 100% compliance. Surveys in various countries, including the US, UK and Canada, indicate that up to 35% of those surveyed indicated that they won't get the vaccine. Another big issue is worldwide-timing. If vaccines are only provided in richer countries, then those who cannot afford it are basically a reservoir for the virus. If we take another year to vaccinate them, it will be a full year where new variants can rise.

But even if just focus on local issues (and I want to emphasize that this would be really stupid to address a pandemic), we can do a little bit of a back-of-the-envelope calculation here. Let's focus on vaccination as the sole measure and let's assume we need ~80% immunity in the population to reach herd immunity.

Let us further assume that the vaccines have an effectiveness of 90%. In order to achieve 80% immunity, it would be necessary to vaccinate 89% of the population to reach the herd immunity target. Only few countries (according to polls) are at that level of theoretical compliance. If we use US polls as an estimate of vaccine willingness (~75%), we can estimate that with a 90% effective vaccine we will have ~68% immunity, lower than almost all current estimated requirement for herd immunity. 

If the vaccine effectiveness goes down to 80% (due to variants for example) we would need to vaccinate every single person. So even if there are no barriers to providing vaccines to folks, it is tricky to rely on it alone to push down viral numbers to a degree that there is no net transmission. 

So no, based on the current situation I actually do not think that the current rollout in practice is likely going to eradicate the virus completely. The more likely scenario (I believe) for now is that it will become endemic. However, the optimistic scenario is that it will be better controlled via regular vaccines (and treatments) and won't have the same horrible death toll in the future. It might indeed become something like a flu, which, I want to emphasize has regularly costed many lives and is not really harmless either (though compared to COVID-19 it is comparatively tame). 

And as a minor sidenote, I would like to emphasize how behavioral changes have affected flu-related deaths. In the years prior 20-50k folks are estimated to have died each year from influenza in the US. Last year  it was a few hundred reported so far.

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  • 2 weeks later...

Just to add to the issue of variants.  Even if vaccines are effective against the new variants, there is the issue that by now it is pretty clear that they have a higher transmissibility. B.1.1.7 has effectively replaced the wildtype and has up to 90% higher transmissibility. Based on preliminary studies B1.617.2 seems to be even higher (and in places is starting to replace B.1.1.7).

The reason why that is relevant is that a higher level of immunity within a population is required to deal with a higher transmissibility. A value to indicate the ability to spread is based on the basic reproduction number (R0) which is the average number of folks infected by a given infected person within a susceptible community. The effective reproduction number (Re) is then dependent on the susceptibility (s) of the population, taking e.g. immunity due to vaccination and other measures into account.

I.e. Re= s*R0.

In order for the disease to vanish, the effective reproduction number needs to go below 1. As the immunity in a population is given by 1-s we can then look for

1-s > 1-1/R0 to estimate how much immunity we need for that to happen. 

Originally the R0 for the wildtype SARS-CoV-2 was estimated to be around 2.5, which would require only 60% immunity in the population to stop. However estimates with larger data sets (and with the unknown impact of undetected spread) have put R0 quite a bit higher (3.6 and up), which would require over 72% immunity to achieve herd immunity, with estimates as high as 84%

Now if we increase R0 even higher for B.1.1.7 and B.1.617.2 we are approaching required immunity levels of 90%, which is basically impossible to achieve just by immunization.

 

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