Having a titer done will not help if, as some suspect, it is the needle injury itself that causes the sarcoma. The actual vaccine is still perfectly safe—unless you have a cat who has had an autoimmunity disease. I had a cat who barely survived a devastating autoimmune disorder, and I never vaccinated her after that out of concern that it would trigger another autoimmune episode.
Between 1 in 1,000 to 1 in 10,000 cats develop fibrosarcoma as a result of needle punctures. Compared to the chance of getting some horrid infectious disease, that is still fairly low.
I have not checked animal vaccine development to see if nasal or other non-injected forms of the vaccines are being tested. It would be nice if they are; it certainly would make a lot of cat parents happy.
Having had a diabetic, with no other problems, I don't think I believe that a needle injury causes a sarcoma.
I injected my cat sometimes more than twice a day, using a sliding scale not unlike human diabetics use, to dose. He also got sub Q's for awhile. Never a problem.
On the other hand, I have never been big on vaccinations. My cats are all indoors only so all they ever got were the kitten vaccinations.