Why IV medicine need to go into a vein, when a vaccine can go anywhere
Oh my how to answer this one? A vaccine can't just go anywhere...it has to go into a muscle. If it went into your vein it would be absorbed far too quickly and could cause you harm. Some medicines can be given IV and IM routes but it depends on how fast and how sick the person is. Generally the muscle route will be more painful but in the instance of antibiotics, you will get the medicine more quickly and if you have a very severe infection, say meningitis, it could save your life. Things like vaccines, tetanus shots are only given by muscle because of the absorption rate and is recommended by the manufacturer. Sometimes antibiotics or painkillers are given either IV or IM but that is chosen by the prescribing physician or suggested by the nurse. Then, to confuse you even further, some compounds just aren't made to be given in an IV and must only be given via muscle. Does any of this make sense?
IV medication needs to be distributed through the body quickly hence using a vein. Vaccinations need to go into muscle to ensure slow distribution.
"IV" medication refers to "Intravenous", which means, uh, going into a vein. So, in definition anything that is "iv" (which can include some vaccines) is designed to go into a vein.
Vaccines are developed with different routes of administration - such as orally, intramuscularly, etc.