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It has to be delivered intramuscularly. Any large muscle group will do, which is why we have a few spots to choose from - the upper arm, hip/glute area, thigh. Upper arm is easiest to do in the clinic typically although it's not abnormal to be asked to pull your pants down for shots! You can get more than just vaccines delivered via intramuscular route. Efficacy would be affected, yes, if the vaccine just gets into thick skin layers like in the foot.

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Would the center of the sole of the foot be an appropriate place to administer? I’ve heard of some people getting a BCG vaccine there due to the likelihood of it leaving a scar on the arm. Would that decrease efficacy?

Vaccines are administered into a muscle because its a highly vascularized tissue. This means there’s a lot of blood vessels that supply muscle. Therefore, the vaccine can become detected by the immune cells in your blood and your body can initiate the immune process. You want to avoid administration into fat tissue because it is not as vascularized, leading to delayed absorption and possible denaturing (or breakdown) of the vaccine. The deltoid muscle of your arm is a great spot because it often has only a thin layer of fat and a thicker layer of muscle. This site has also been shown as a safe route because of the relatively lower risk in puncturing a major nerve. If you were to inject into something like a foot, you run the risk of missing a muscle and/or puncturing a nerve.

Would be super inconvenient if you get swelling and/pain.

Efficacy is impossible to know if not tested.

Amount of blood vessels in area aka vascularity decides where would we administrator any parenteral product which includes vaccine. We want to it to get dissolved in blood to show it's effect, if there are a lot of blood vessels the distribution of vaccine/medicine will be faster. But vaccine isn't injected into blood directly since it's a killed antigen Or it's byproduct or any other live antigen, we want it to act slowly so given intramuscular, because if it went directly in blood the action will be faster that's the side effects I'm talking here like fever, etc who are going to cause problems. I've not heard or seen anyone administering vac in foot area though.

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BCG is not given intramuscularly, it is given intradermaly. From what I remember, an intradermal injection is given by inserting the needle into the first few layers of skin and then the injection is made in a pocket within the skin. Sometimes I think they will even insert the needle and then lift it to help form the pocket

If BCG is given subcutaneously (below the skin) then it can be dangerous to the patient

So it makes sense then that BCG could be given on the foot since it’s within the skin and not the muscle

Source: https://en.m.wikipedia.org/wiki/BCG_vaccine

>Any large muscle group will do

This is not always true, even if it applies to covid vaxes. Muscles vary greatly in their receptor expression.

Gonna hop on the top comment early to let people know not to let them jab your shoulder. I am taller than the person giving me my flu shot and it resulted in a weird angle that lead to them piercing my rotator cuff. Ended up with 2 months of rehab before the pain subsided.

I realized they cleaned a place high on my arm, but no one ever warns people to make sure it's in the deltoid* and not higher. Edit: wrong muscle

Vaccines are usually delivered via the intramuscular route. It's all about how the vaccine is taken up by the body. Training focusses on the upper arm and thigh, though the upper arm is by far the most convenient. There are other benefits - there are comparatively few nerves in the upper arm muscle, which is why people often feel very little. Those that refute that, well you just got unlucky and the vaccinator hit a nerve. If the vaccinator hits the bone (usually a lack of muscle tissue) you would not know.

The exception is some people (eg young children) may have vaccines delivered through the nose as a spray or drops. This is also linked to efficacy of delivery.

There are always exceptions, but delivering a vaccine other than the intramuscular route would not be a licenced use of the product. So yes, there are legal reasons too!

The injection is not supposed to be into the bicep. It's supposed to be into the deltoid.

Thanks for that, the important part is no shoulder lol.

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you don't get to sit down for your shots? sorry that happened to you. I usually assume doctors know their anatomy

We sat, I'm 6'3, they were less that 5' so it was still an odd lean. It was a pharmacy tech instead of a doc. Some areas trained them for vaccines due to the sudden demand.

p sure it had to be a doctor here. I'm pretty tall (almost 2m) the person giving the injection always stood during my jabs

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Honestly doctors don’t give shots. Nurses are much better trained and I would trust them over a doctor

Interesting, I didn't know about this! Do you have any more detail on that?

You’re not trying to get your vaccine into the muscle cells themselves. All the action happens in the draining lymph nodes.

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To my understanding you're trying to get it absorbed into the bloodstream, which is why you aim for muscle which is highly vascular tissue

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Any research why not intravenously?

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Doctors are perfectly capable of giving an intramuscular injection. It doesn't take longer than an hour to learn how to administer them and even that is being generous.

But you're definitely correct in that it does not happen often that doctors give shots especially in a hospital setting.

EDIT: for intravenous injections I would agree with you as nurses (depending on which specialty) are a lot more experienced and do this much more regularly than doctors.

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The pharmacy tech giving shots is a new thing spurred on by COVID. Before then it was always the pharmacist.

Am pharmacist

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You don't want it in the bloodstream, and they're even supposed to check that they don't accidentally enter a vein by aspirating before administering the vaccine dose.

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That’s out of date practice. Some people may teach to aspirate but it’s unnecessary.

Agreed, physicians are definitely capable of giving an IM shot, but rarely do. This may have been a thing a long time ago, but is not done (at least in the US) currently. Source - have been a practicing physician for twenty years.

It’s like starting an IV - the only docs that are good at that are anesthesiologists. They even know how to set up the pumps, mix IV meds, etc. if someone were crashing and needed an IV and infusion started, and I was the only one there to do it, the prognosis would be poor.

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Not sure who gave me my flu shots or shingles shots pre-Covid. I presumed a pharm tech, but it may have been the pharmacist.

The deltoid is the shoulder muscle. Anything 2ml and less can be appropriately administered in the deltoid. It would be highly unusual if not impossible for them to enter into the joint space with the needles used for a IM injection. Additionally, even if they did it would have no effect on your rotator cuff, which is just a group of 4 muscles. Its not one physical structure like most people tend to assume. You need at least a 1.5 inch needle to enter into the glenohumeral space, the needles in IM injections are usually 1 inch or less and they are not going all the way through l. I'm 6'5" and I've never had an issue getting an IM shoulder injection. I also do joint space injections all the time and you have to be very specific in where you aim and how to even enter into the space as the acromion blocks most of the joint off.

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Just to add, children's vaccines are almost always given in the thigh, which apparently reduces common side effects.

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So why is it delivered intramuscularly and not into the blood? How does it work when it’s injected into the muscles to spread throughout the body?

I can't speak to how it would affect the vaccine and the body's response to it, but I can say that giving a vaccine Intravenously is impractical and potentially dangerous at scale. I work in an ER and it can easily take 20+ minutes to start an IV on a patient, especially if they're very young or very old. That's compared to administering Intramuscularly which will take 2 or 3 minutes at most. From what research we've done on vaccines, doing it intramuscularly is perfectly fine so there's just no reason to change that. There's also a greater risk of sepsis going from IM to IV since you're opening a path directly into your bloodstream instead of just near it (again I can't speak to whether or not the vaccine itself would cause issues, but I can't imagine it would help).

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There's overlap between medications and some medications can be given either way. However IM is going to be a slower release over time versus being immediately introduced all at once into the bloodstream. I know the form of medication or the substance it comes in plays a role too, some play better with different tissue types (some meds we give into the fat tissue as well depending on absorption). There's also the issue of bleeding risk which would be higher trying to give something IV when it's safer in a clinic setting to just give it IM. But as far as I'm aware the biggest factor is the more controlled release time

So basically their story is crap is what you're saying?

Why IM instead of IV?

Which is why we make people sit down and landmark correctly. Up to 2ml in the deltoid. Find the acromion process and palpate the deltoid. Use the z-track method of injection.

I don't doubt that nurses could do it, but here in Germany vaccinations are administered by doctors, even during the pandemic. Never got one by anyone else

You see that's the thing, the Deltoid is the shoulder muscle. You definitely want the injection into the shoulder, because that is where the Deltoid muscle is. Just, into the muscle, not anywhere else like the joint capsule or whatever.

This is correct but the glute area is in some cases frowned upon due to the depth of subcutaneous fat potentially being too deep to ensure intramuscular injection. For example the rabies vaccine is to not to be injected in the gluteal area. Don’t wanna risk depositing the vaccine in fat when it comes to rabies!

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It's about how the vaccine is taken up by the body. IM is a much slower release than IV which minimises reactions, especially anaphylactic shock and more serious side effects.

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Because you don't want inflammation response to vaccine speading through your blood stream and causing inflammation all over your body. That's how you get cytokine release syndrome, go into shock, and die.

You want a vaccine to cause a localized inflammation reaction (somewhere harmless, like an arm), recruit immune cells there, have them sample the antigen (vaccine), find ones that bind to the antigen, cause their proliferation, and as a result develop immunity to the disease. Your immune cells have a mechanism to be recruited out of the blood, lymph, and surrounding tissue and to get to the location of inflamation. Vaccination utilizes this mechanism. Vaccines are also specifically tested to work only through their specified method of administration, whether that's intramuscular (like most vaccines), nose spray (like flu mist), oral (like rotavirus), or skin administration (like BCG). Spraying regular flu vaccine into the nose won't work, just like giving it orally. It's formulated to elicit correct immune response only when it gets properly administered. The reason for this is more complex immunology.

Seriously?! I had no idea! Is there an article I can read on that? I've taken basic immunology, but that wasn't covered.

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Because you don't want something immunogenic circulating in your bloodstream. That's how you get cytokine release syndrome, shock, and dead patients. You want localized immune reaction somewhere safe (like an arm), where immune cells can be recruited to from blood , tissue, or lymph; to do their thing.

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That’s an interesting difference in practice. If a patient needs an IV bolus of a medication, does the physician also do that or is it delegated to a nurse?

Thank you that’s super interesting

Thank you, that’s super interesting

One reason recently is illustrated by the rare cardiac side effects from the various Covid vaccines. There's evidence to suggest that the virus' spike proteins themselves can cause damage to cells even just as non-functional fragments. So a sore and inflamed arm muscle from your deltoid muscle cells reacting to the spike proteins is fine. But if your heart gets hit by a bunch of Covid Spike proteins and gets inflamed that may be what's causing myocarditis even though they aren't being infected by a virus.

https://newsroom.heart.org/news/coronavirus-spike-protein-activated-natural-immune-response-damaged-heart-muscle-cells

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Every time I've gotten a shot at a pharmacy, it's been the pharmacist that administered it. I didn't think techs were allowed to.

You didn't mention one very important thing: research. To reguster a drug, You need data backing it up, either as safe and effective or noninferior to another similar drug(which is to say, it's not less afe and efficient).

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The vaccine itself isn't meant to spread through the body. What it does is activate immune cells that were already hanging out in the muscle (generally macrophages), and those activated immune cells release chemical messengers called cytokines to call other types of immune cells to the site.

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Thank you

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At least for the mRNA vaccines, intravenous injection could be dangerous. In a mouse model, intravenous injection of the vaccine caused myocarditis, so accidental intravenous injection has been suggested as cause for vaccine-induced myocarditis.

https://pubmed.ncbi.nlm.nih.gov/34406358/

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Do the spike proteins from the mRNA typically remain local in deltoid muscle or do they distribute in significant quantity around the body?

I'd always assumed injection site pain was due to the "injury" of being stabbed with a needle, but it makes more sense that it'd be due to a localized immune reaction.

Nope, the needle they use is thin enough that if there wasn't an inflammation, any pain would be minimal (think how long the puncture site hurts after a blood draw.

What hurts is your immune system reaction to the vaccine or it's components (adjuvants) itself, because that's necessary for immunizing against the antigen.

I believe that's still a point of interest without a definitive answer. There are studies which showthere is circulating spike protein. There are studies which show similar levels of S Protein circulation between vaccination and infection. But there are also studies showing that infection causes higher rates of myocarditis. Both could be true (Spike Protein could be one cause of myocarditis and the higher rates of myocarditis in infected patients being due to compounding causes in addition to the circulating S protein.) But I don't think there is even a definitive answer yet on whether the spike proteins are exclusively responsible for all of the vaccine induced myocarditis.

Thank you for the links and answer!

I wonder if the LNP’s may be behind some of the cases. There was a possible vaccine-induced myocarditis in the Novavax trial, which are LNPs with recombinant protein S. Although the the fact that it contains protein S may be confounding.

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> noninferior to another similar drug(which is to say, it's not less afe and efficient).

A new drug can be inferior in some ways, provided it is better in others. For instance, if it is a lot cheaper, has fewer side effects, targets a sub-group not covered by the comparison or more easily made available.

For instance, medications suitable for pregnant women are often inferior (less effective) that comparisons.

Anyway, words are fun. You can make them mean whatever you want.

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For some reason, I read that as "Thanks you're super interesting"

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I assumed it also had to do with babies utilizing their arms more in general but largely to feed, cling, and pull themselves (army crawl). Sore arms would be stressful for baby and parent.

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