*Long thread warning*

Because people seem to be confused I thought I could throw in my own explanations about the possible effects of vaccines on transmission. Let's imagine an arbitrary scale of vaccine efficacy for a minute, like this one that I made up:
Let's now consider what the absolute perfect vaccine might do on this scale.

Well ideally, the immune response it induces is so rapid and so robust that it is able to keep you from even getting infected. This is called sterilizing immunity.
Sterilizing immunity does not have anything to do with sterility in the reproductive sense; it refers to being able to maintain a sterile (i.e. not contaminated) environment. This is as good as things can get. Why don't we just make all of our vaccines do this?
Well, for one thing it's really hard. It's actually a very unnatural outcome in some ways. Most infections don't produce sterilizing immunity. There are also other immunological challenges to be overcome. For example, the immune system actually has different compartments.
Your mucosal surfaces are directly exposed to the outside world, but the immune system at these surfaces acts differently from the immune system inside your body. It can be hard to ensure systemic responses cross over into the mucosal compartments like the upper respiratory tract
There are a few reasons for this but I want to keep this simple so you can read these for more information if you want details on why it's so hard:
sciencedirect.com/science/articl…
nature.com/articles/nri17…
jimmunol.org/content/199/1/…
It's important to note however that this isn't universally the case. For example, antibodies from the blood have a very easy time getting into the lungs, which means you can reliably protect people against pneumonia quite well- but the upper respiratory tract is more difficult.
Sterilizing immunity is awesome because by preventing infection, you can also prevent any opportunity for the pathogen to mutate. But you also miss out on the boosting effect to your immune response from encountering the pathogen.
At the opposite extreme, you can have what's known as a leaky vaccine. These aren't ideal but they're better than nothing. The concept behind these vaccines is they produce incomplete protection in vaccinees. This protects them against severe disease.
The major reason these aren't great is that these still allow for productive infection of the host and give pathogens an opportunity to mutate and escape the immune system. Many vaccines intended for livestock are said to be leaky.
It's harder to point to an explicit example of a leaky vaccine in humans. Some propose that seasonal flu vaccines count but I'm not sure they fit the definition perfectly.
But guess what- a leaky vaccine would still be really valuable against a raging pandemic because it would keep people out of the hospital and reduce strain on our medical systems. But then there's the question- does it disrupt transmission?
Actually- yes!

nature.com/articles/s4157…

Even leaky vaccines prime the immune system and thus can reduce the pathogen load and therefore lead to reduced transmission, and potentially reduced disease severity (possibly because of an inoculum size effect- more shortly).
You can also imagine that asymptomatic individuals (like those who may have gotten a leaky vaccine) are less contagious than those who might be e.g. coughing and shedding virus all over the place.
Okay, so if these are the two extremes, where are most of our vaccines? We do seem to get sterilizing immunity with the HPV vaccine.

But most of our vaccines live somewhere in the middle, closer to sterilizing immunity than to leakiness in my arbitrary scale. Let me explain.
When you are exposed to an antigen (something the immune system can recognize- for our purposes, a virus/bacterium etc), if you encounter it again, it triggers a secondary immune response. This response is more rapid and larger in magnitude than the first encounter.
So in the context of a virus or bacterium, an infection is initiated and some replication occurs, but the immune response kicks in rapidly and arrests the process. This could mean that you have no symptoms or very mild symptoms and they should be shorter lived.
This should still result in significantly reduced transmission. The reason is that it generally takes a lot more than one particle of the virus/bacteria to cause disease (some exceptions though).
By having a rapid recall response from the immune system, you may never get to a point where the viral load in the relevant anatomical site builds to a level that can be passed to others and cause a productive infection.
Alternatively, the time you spend in a contagious state may just be very short lived because of your immune system's quick actions. It's thought that most of our vaccines work like this- this results in reliable prevention of disease in most vaccinees + less spread.
So, now you're wondering- if this is all true, why can't I just toss my mask after I've been vaccinated against COVID?

It's complex. Firstly, the most basic reason is that it takes time for a herd effect to build up in the community.
It is unlikely that these vaccines confer sterilizing immunity if only because of how rare that is- but that's still okay. We can still drastically reduce the transmission of virus throughout the population even without sterilizing immunity (as this thread hopefully shows).
The other issue we run into is the problem of the asymptomatic carrier state. While it's true that asymptomatic individuals are less contagious than those with symptoms in COVID-19, this isn't the same as them being not contagious at all.
If enough people just abandon precautions before we reach that level, we will see a spike in COVID-19 still.

@nataliexdean really knocked it out of the park with explaining this aspect so here's her amazing thread:

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More from @ENirenberg

22 Feb
If anyone is confused about what sealioning looks like, here's a really excellent example.

Multiple physicians, including pediatricians and infectious disease specialists, have presented evidence showing this assumption is incorrect. But he's "just asking questions."
About half of pediatric flu deaths occur in previously healthy children.
pediatrics.aappublications.org/content/132/5/…

Here's a summary on the 2019-2020 flu season in kids:
cdc.gov/flu/spotlights…

Feigin and Cherry's Pediatric Infectious Diseases also notes the following:
In other words, flu often doesn't act alone. Co-pathogenesis with bacteria is not all that rare, and the virus itself provokes immunological derangements and can remodel the microenvironment of the respiratory tract to promote disease.

nature.com/articles/nrmic…
Read 16 tweets
30 Jan
Let's talk about the US's vaccine adverse event reporting system (VAERS), with emphasis on its misuse by bad actors.

VAERS is a self-explanatory system. I mean that literally: it tells you exactly how to use it (and how not to).

VAERS is a spontaneous (passive) reporting system. Anyone can submit a VAERS report, and certain events for certain vaccines are required to be reported by healthcare providers under the NCVIA law. Herein however lies one of the limitations.

cdc.gov/vaccinesafety/…
As an adverse event is anything bad that happens following the receipt of a pharmaceutical, it need not be causally related to the vaccine. If you look hard enough you can find VAERS reports for things that are obviously unrelated. For instance:
Read 17 tweets
20 Dec 20
I have a bigger audience now (still don't get how that happened) than I'm used to so I need to clarify some things about me.

Firstly, I am not a public health expert, nor an expert on COVID-19, pandemics generally, virology, infectious disease, or medicine.
I have a BSc in Biochemistry and I did a lot of coursework in immunology at a fairly high level and some labwork and journal clubs therein too.

It would also be delusionally hubristic of me to claim that I were an expert in either immunology or biochemistry or vaccines.
I know some things and have some experience with them.

I am comfortable enough with these things that I can pick up most papers about them and have at least a basic idea of what's going going on. I might also be able to offer criticism if it's a topic I am very familiar with.
Read 13 tweets
20 Dec 20
Some reminders after a disheartening thread:

- Depression is a real psychiatric condition that in addition to cognitive and emotional hallmarks produces changes at the cellular level within the brain and may include pharmacotherapy as part of a treatment plan.
- Behaving as though there is artistry and meaning in a person's suffering to get them to revel in it and neglect their wellbeing, furthermore as a means of remuneration, is grotesque and depraved. Feigning innocence and ignorance at being confronted with this truth is shameful.
- Antiretroviral therapy saves lives. Good compliance with ART can lead HIV patients to a normal life expectancy and prevent transmission of virus to partners. Convincing people not to take indicated ART robs people of years they could have spent with loved ones.
Read 5 tweets
17 Dec 20
I've seen a bunch of people talk about vaccine hesitancy lately but the people doing it seem to be getting some important things wrong.

Firstly, vaccine acceptance is a continuum, as shown in the attached image.

My good friend, @lizditz has a post:
lizditz.typepad.com/i_speak_of_dre…
Most people fall somewhere in the middle. You generally don't see people calling for no vaccines at all, and it's relatively rare for someone to unquestioningly accept all vaccines.

Those people in the middle, they are hesitant.

Messaging about vaccines should focus on them.
That said, the people in the far left of that diagram are what some people might call "anti-vaccine."

This term for some reason has invited a bunch of controversy in its use. I don't think there's anything wrong with the term, but I do think many use it incorrectly.
Read 21 tweets
15 Dec 20
So I'm told that there's some confusion going on about what placebos for vaccine trials should be.

Let's chat about this one.
It's really common to hear from anti-vaccine people that a lot of vaccines are not tested against "true placebo," which is saline apparently.

This is a fallacy with many components to it.
Fundamentally the point of a placebo is to give you information about whether or not a treatment works.

There are a lot of different kinds of placebos; in vaccine trials it's a sham treatment- something that looks like the vaccine but isn't.
Read 16 tweets

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