Answer: First of all, a vet would not be able to tell from examining the cat whether or not it has been vaccinated against the usual infectious diseases; unless, of course it is showing obvious signs of one of them which would strongly suggest that it has not recently been vaccinated against it.
It is possible to measure the level of the antibody in the blood against a particular organism, although this won’t tell you whether it is the result of vaccination or natural infection; not that is matters because the immunity would be the same. However, this type of test is not done routinely and would be transfer to difficult to arrange and expensive, particularly since it would need to be done separately for each disease.
More importantly, it would be unnecessary to go this trouble and expense science routine vaccination would be cheaper and would not prove harmful even if it was quite unnecessary. However, care is needed if your stray cat is found to be pregnant because, as mentioned previously, it is inadvisable to use live vaccine at this time.
