After a dog bite, why are vaccines given in multiple injections rather than a single injection containing multiple vaccines?

Question

When a dog bites a person, why is it necessary to take about 5 injections or needles? Why not just one big injection?

Do they all have the same medicine? Or does each one have its own medicine?

Is the time between them important? I see on the internet different periods such as (the first one should be taken immediately, the second one is after 3 days, then once per week) and you can find other different sequences.

My research is:

1. The immediate vaccine is human rabies-specific immunoglobulin (HRIG) and this explains the first shot. Vaccination is also for Rabies, Tetanus, and maybe some other bacteria. For me, this means one or two more injections. One for Rabies and Tetanus and One for the other bacteria or whatever the combination is. This is a total of 3 injections including the immediate one. So why the 5 injections? I mean what could be the other diseases/bacteria?

2. Is it possible to take all the vaccines through one big shot? I know it depends on the amount/size of each vaccine. Or maybe it is required to wait for a few days to reduce the side effects or whatever the reason is, right? This source compares dog vaccine to human vaccine so it's not that related and I can't find useful sources. I'm not talking about inventing new techniques like this one. I just wonder why don't we combine/mix the 5 or 6 injections together.

3. The number of injections vary from one case to another. That's why I think that only the first injection has a different solution but the other successive injections have the same solution/medicine, right? At the same time, some sources say these successive injections are different because they are for different medicines like Tetanus...etc. So I got confused.

4. I knew the answer to the third question. Yes, the time is important and a delay of 1 to 2 days is considered acceptable as your antibody levels will still be high enough to fight off an infection.

Answer 1

Brief background

There are 2 major types of vaccines, passive and active vaccines. Passive vaccines are simply "antibodies" to fight off disease and active vaccines are "dead/weakened/components(e.g. proteins)" of the offending agent to allow your body to produce your own antibodies.

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Same is true for anti tetanus, (which may come in different mixtures) tetanus toxoid is an active vaccine which is given to adults if it has been 10 years from your previous booster or unrecalled date of the last dose. Tetanus immune globulin(igtet) is the passive form. For anti-rabies, we use ARV(anti-rabies vaccine/active) and ERIG/HRIG(passive vaccine)

-HARRISON'S principles of Internal Medicine 18th ed Tetanus pg. 1199

In short, you may take at least 2-4 injections depending on your previous vaccinations and what category your animal bite injury is.

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Mixing vaccines in one syringe

"No vaccines should ever be mixed in the same syringe unless the combination has been specifically approved by the FDA." -immunize.org

 

It is prudent to give in separate limbs (if possible), so there is no confusion about which vaccine caused an allergic reaction. -immunize.org

 

"Diluting or mixing a biological product with other components or repackaging a biological product by removing it from its approved container-closure system and transferring it to another container-closure system is highly likely to affect the safety or effectiveness of the biological product" -FDA link to FDA protocol, PDF file

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Giving vaccines on a schedule _{(lifted from OP's provided link)}

"The rabies vaccine is made up of the dead rabies virus. When it is injected into your body, your immune system it immediately starts to produce antibodies to fight off the perceived infection. Multiple shots ensure that the levels of antibodies remain elevated so that even if the live virus is already in your system, the antibodies will neutralize it."

-HARRISON'S principles of Internal Medicine 18th ed Rabies pg. 1615

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References

Cdc.gov, immunize.org, who.int, fda.gov

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P.S.

The anti-tetanus vaccine schedule is in the provided link and I lifted the answer from OP to give a short preview of the answer. A total of 3-5 injections if we include antibiotics.