The question to which I was responding was a general one, and didn't pertain specifically to influenza. Now, on to your question...
Vaccines do exist for the flu, it's just that they are not completely protective because the virus easily mutates, and thus there are many different strains circulating each year. Only those that are expected to be the most prevalent strains for a particular season can be placed in the vaccine.
Now even if there is absolutely no vaccine for a particular respiratory virus (such as in the case of SARS), protective measures can be taken. There is a reason many folks in areas affected by SARS were wearing hospital masks during the height of the scare. If you don't inhale any infected aerosols, then you won't become infected with the organism.
All measures aside, there is no way to guarantee 100% that a person will be able to avoid contracting a particular disease, simply because that would require testing an infinite number of possibilities. New methods of transmission may develop, and breakdowns in public health measures do occur. I get the impression that you want to be told "Do this, and you can't get sick with this bug, no matter what." That expectation will only lead to your frustration.
No, actually, I was being sarcastic. I think it's dangerous to assume there are effective ways to avoid respiratory (airborne) viruses. I know there are flu vaccines and of course the way flu mutates you might not be covered by what you've been exposed to in the past.
There are also viruses that can stay active in the environment for months (fortunately, flu is not one of them). All you need to do is come in contact with them by whatever means, and you'll get sick. No amount of avoiding sick people, etc., will do you any good.
That said, there ARE techniques under development for far more robust and speedy vaccine development--so I'm not a doom-monger on this either, necessarily, but I do think the public underestimates the hazard, media hype notwithstanding.