Why do vaccines cause some people to have seizures and paralysis?

Question

Is it the needle that they react to, or is it something to do with their nervous system?

Also, why can't we just ingest the vaccine via mouth?

Answer 1

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I'm not aware of vaccines causing paralysis, unless someone erroneously hits a nerve with a needle. Some people may have an allergic reaction to the vaccine, though, which could lead to seizures.

Most vaccines cannot be ingested by mouth, because the digestive system would destroy the vaccine's contents before the immune system could respond to it, making it useless. Truth be told, we'd prefer to give them orally if we could.

There is an oral polio vaccine, which is used in developing countries. Developed countries often don't bother, because the injected one is probably somewhat more effective, and we just put it in the same needle that all the other vaccines are delivered in.