As an actual vaccination strategy, introducing an immunological challenge via the respiratory mucus membranes is actually probably a good idea. There really should be a two step process to it though, as a normal respiratory infection first encounters the pathogen in the mucus membranes of the respiratory system, antibodies to the pathogen are generated there (in the mucosal membranes) primarily as IgA. There is also research (that I can't seem to find at the moment) that looked at small lymph node like structures in the intestines, that were previously thought to be useless, that take the antigens that your respiratory system produces and ensure that you don't become self reactive. So, a vaccination strategy that used a nasal spray first, followed by an oral solution containing the antigens might be best. However, there really isn't a way to determine exactly what antigens the body will produce, so the oral part becomes potentially impossible, other than naturally by swallowing the actual antigens themselves. An injected vaccine primarily produces IgG, which circulates in the blood stream. It's a different part of the immune system entirely, the ability of the lymph nodes in the gut to react to the produced antigens is bypassed and the likelihood of self reactivity (auto-immunity) is increased. What this effectively all boils down to though, is that it is best to get a mild form of the actual infection in a natural way (i.e. the pathogen is presented to the body as it would naturally be). For most diseases, this means just getting it (cold, flu, etc.). Ensuring that your innate immune system is working effectively will have much more effect on the outcome than any prior artificial "vaccination". A vaccination is not necessarily a good or bad treatment, it's just a treatment. The level of understanding of the people making it, their care in making it and their intent (are they making it for the betterment of people, or are they making something to make money or gain control) are key, in vaccines as in other medical treatments (cf. opioids). Currently, the pharmaceutical industry as a whole and much of medical research and academia are fatally compromised, there is no promise or statement that they can make that can be trusted in any way.