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Regarding Herd immunity.

xoggyux

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So I have been seeing a lot of people, many within the healthcare field but others in the news/tv/media/journals talking a lot about herd immunity.
My baseline knowledge of epidemiology is rather basic, just the couple lectures sprinkled in during medschool, but every instance of herd immunity that was taught to me was in the context of a large population that already has immunity (either via prior infection/recovery or vaccination) and this protects people that are unable to acquire this immunity due to weak immune system, contraindications for vaccines or inability to produce adequate immunological response after exposure to a vaccine/antigen.

In the current context of a pandemic, I am having a hard time trying to visualize how herd immunity could be of any help. My understanding that herd immunity is taking advantage of a low prevalence of a disease (because most of the population is immune) and the lack of vectors (for the same reason, most of the population is immune). But in the case of a pandemic, just the fact that most people need to go through the disease to develop immunity guarantees that the prevalence won't below and that there will be plenty of vectors. It is hard for me to imagine that 70% if people will get infected but that somehow the other 30% will get spared because "herd immunity".

I guess it might depend on how fast is the growth in case, I suppose if you can prevent exponential growth curves you could end up with a low prevalence by the time that a sizable percentage of the community is already exposed, but in the case of a pandemic, this could take years if not decades to spread to millions of people in this fashion.

I just wanted to see what are your thoughts and if I missed something.
 

shouldigomd

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I don't think it would take decades.... heck the vast majority will be exposed by 6 months most likely.

Herd immunity is the natural course of a virus like COVID. This idea was embraced by sweden who protected their elderly / at risk population while allowing the young / healthy to mingle. Now with a majority of people having been exposed and now immune those virus naive people have a lesser risk of contracting.
 
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chessknt

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Nobody knows if herd immunity can even work. It may have seasonal mutation and everyone may be at risk again. There may not have good immunological memory for the virus and immunity won't be sustained. The antibodies formed from immunity might not prevent infection etc etc. Not our job to figure this out unless you're a research immunologist and anyone who says they know what is going to happen is speaking from a position of ignorance.

For an n of 1 I saw a patient who had covid 1.5 months prior who came in with covid symptoms and had covid again. Since she improved and was out of the hospital for a month before I'm assuming this is reinfection with the same virus or a mutated reinfection but either way her immune system failed her. We don't have enough data from survivors to know how widespread this phenomenon is.
 
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blub1212

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The big unknown here is what the immunogenicity of this virus is. Working towards "herd immunity" is kind of a moot point if survival of an infection only confers short-term protection.
 

tantacles

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So I have been seeing a lot of people, many within the healthcare field but others in the news/tv/media/journals talking a lot about herd immunity.
My baseline knowledge of epidemiology is rather basic, just the couple lectures sprinkled in during medschool, but every instance of herd immunity that was taught to me was in the context of a large population that already has immunity (either via prior infection/recovery or vaccination) and this protects people that are unable to acquire this immunity due to weak immune system, contraindications for vaccines or inability to produce adequate immunological response after exposure to a vaccine/antigen.

In the current context of a pandemic, I am having a hard time trying to visualize how herd immunity could be of any help. My understanding that herd immunity is taking advantage of a low prevalence of a disease (because most of the population is immune) and the lack of vectors (for the same reason, most of the population is immune). But in the case of a pandemic, just the fact that most people need to go through the disease to develop immunity guarantees that the prevalence won't below and that there will be plenty of vectors. It is hard for me to imagine that 70% if people will get infected but that somehow the other 30% will get spared because "herd immunity".

I guess it might depend on how fast is the growth in case, I suppose if you can prevent exponential growth curves you could end up with a low prevalence by the time that a sizable percentage of the community is already exposed, but in the case of a pandemic, this could take years if not decades to spread to millions of people in this fashion.

I just wanted to see what are your thoughts and if I missed something.

In the case of a highly virulent virus, herd immunity could very well occur. That being said, we don't know what the natural course of this virus is, and we're not sure if getting this virus actually confers immunity at this point. If we knew that 90% of people who got this virus were subsequently immune to it, then things might change. However, we're creating a ton of tests right now to figure that out. Do antibodies actually confer true immunity? We don't know! Can you be reinfected after having this virus once? We don't know! Is there even a sustained immune response in the majority of people? We don't know! Will there be a seasonal variant that decreases the impact of immunity? We don't know!

So I suppose the overall message is that we don't know!
 
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DrSnips

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For an n of 1 I saw a patient who had covid 1.5 months prior who came in with covid symptoms and had covid again. Since she improved and was out of the hospital for a month before I'm assuming this is reinfection with the same virus or a mutated reinfection but either way her immune system failed her. We don't have enough data from survivors to know how widespread this phenomenon is.

That's interesting. I had a similar case where infection control gave me a ton of pushback about repeat COVID testing for the patient, stating that if I were correct it would be "the first person ever to be reinfected with COVID, making it so unlikely as to be pointless to test". I guess they were wrong about it being the first.
 

chessknt

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That's interesting. I had a similar case where infection control gave me a ton of pushback about repeat COVID testing for the patient, stating that if I were correct it would be "the first person ever to be reinfected with COVID, making it so unlikely as to be pointless to test". I guess they were wrong about it being the first.

She had to test negative x3 to get to a SNF where she sat for 3 weeks before coming back with similar symptoms and wheezing. Initially presumed to be COPD with negative COVID x1, retested when she got bumped to ICU for needing too much oxygen and COVID + again. Didnt need to be intubated and got better on steroids in about 4 days back out to floor.

We did away with ID holding the gate to testing around late march. Are they still in control even now where you are?
 

DrSnips

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We did away with ID holding the gate to testing around late march. Are they still in control even now where you are?

For repeat testing they do butt in, especially if you are ordering 3rd tests or beyond on someone who has already tested negative multiple times. But I've had several patients test positive on the 4th swab, so I usually get them to relent after a phone call. I think they are under some sort of administration pressure.
 

jdh71

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I actually wonder about some patients being unable to clear. It becomes a “chronic” issue for them. Plenty of viruses you can’t get rid of. Or can’t get rid of easily. I’ve had a few patients come back to the icu all ****ty again. No evidence of new stuff. I don’t know. It’s demoralizing. I hate this virus.
 

aafisahar

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Shamelessly stolen from a post I saw earlier:

For every one person who dies:

-19 more require hospitalization.
-18 of those will have permanent heart damage for the rest of their lives.
-10 will have permanent lung damage.
-3 will have strokes.
-2 will have neurological damage that leads to chronic weakness and loss of coordination.
-2 will have neurological damage that leads to loss of cognitive function.

So now all of a sudden, that “but it’s only 1% fatal!” becomes:

-3,282,000 people dead.
-62,358,000 hospitalized.
-59,076,000 people with permanent heart damage.
-32,820,000 people with permanent lung damage.
-9,846,000 people with strokes.
-6,564,000 people with muscle weakness.
-6,564,000 people with loss of cognitive function.

Herd immunity doesn't really work in the context of containing a pandemic. It's a concept first developed for immunization strategies in estimating how many people need to immunized to provide protection to the entire population. It's essentially been coopted by the right in order to justify ending lockdown and halting the wearing of masks.
 
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Spikebd

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Shamelessly stolen from a post I saw earlier:



Herd immunity doesn't really work in the context of containing a pandemic. It's a concept first developed for immunization strategies in estimating how many people need to immunized to provide protection to the entire population. It's essentially been coopted by the right in order to justify ending lockdown and halting the wearing of masks.
The moral of the story, and 90% of medicine, make smart lifestyle choices To stay in the best health possible to give your body every chance it can to beat the virus on its own.
 
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