Exactly, its anecdotal and subjective. That makes it very, very difficult. It'd be more realistic to try to prove titers/protection from a vaccination than prove some of the "diseases" that people are contributing to the vaccine. If protection was proved for a longer period of time, it justifies less frequent vaccinations. that might open the door for investigating soem of the "attributed diseases". I really don't have a set time to answer your second question.