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Roadgoddess t1_j50mu0y wrote

Reply to comment by firstfrontiers in Is there any difference in efficacy when a vaccine is administered somewhere other than the upper arm (e.g. on the foot)? by MercurioLeCher

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?

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firstfrontiers t1_j50ntmt wrote

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

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Bax_Cadarn t1_j51914h wrote

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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Indemnity4 t1_j530irm wrote

> 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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volyund t1_j50zvb2 wrote

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.

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inna_hey t1_j51jjdz wrote

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.

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volyund t1_j51lfmi wrote

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.

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Jaralith t1_j51c6dh wrote

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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