The scientific evidence establishes with a high degree of confidence that vaccines cause serious health problems in less than 1% of recipients, and also don't cause less serious problems in a high fraction of the population.
In serious health problems, we include SIDS (death), ASD, auto-immune disorders, cancer, life threatening allergies, narcolepsy, Chronic Fatigue Syndrome. To claim that vaccines are safe it seems a minimal prerequisite should be that it be established they don't do such serious harm to a significant fraction of the population. Perhaps other conditions should be added, and it would be nice to insist on less than 1/1000 individuals suffering such catastrophic loss, adding together the numbers that acquire any of these serious conditions from vaccines.
In less serious health problems we may include such things as lesser IQ loss. We stipulate that if vaccines are causing an average IQ loss in the population of say 5 points, that would be quite serious to the future of the world. Maybe an average loss of 1 IQ point would be acceptable, but it would be nice to rule out more substantial average loss. We also include such things as Epilepsy, Migraines, Skoliosis, Diabetes Miletus, Asthma/Chronic Bronchitis, Hypothyroid, or a weakening of the immune system leading to substantially greater susceptibility to illnesses such as flu or respiratory illnesses. For example, it would be nice to rule out the possibility that receiving the vaccine series causes a child to have on average twice as many respiratory illnesses as an unvaccinated child would. If parents believed vaccines are causing one or more of these various problems in more than 5% of the population, many parents may reasonably reconsider their decision on whether or when to vaccinate their children, or which vaccines to give them, and physicians and pharmaceutical companies may redouble efforts to make safer vaccines. So we ask whether it may be established as well that this isn't happening.
And also, to establish safety, it would be reasonable to ask that it is established that less debilitating but annoying problems be ruled out as being caused in a high fraction of the population, such as perhaps 25%. This may include Hayfever, Otitus Media, Herpes, Neurodermatitis, Sinusitis, Allergies, Hyperactivity. To say that vaccines are safe, it would be reasonable to demand that the evidence taken as a whole gives a reasonable observer perhaps at least a 90% confidence that none of these three problems is happening.
In addition it might be noted that vaccines exist as a reaction to various catastrophic illness and that considerations of their safety should be weighed alongside the risk associated with these ilnesses and the extent to which vaccines are successful in protecting against this risk. Another diagram has been added discussing this subject http://truthsift-env.qh5iy45he4.us-east-2.elasticbeanstalk.com/search_view?topic=The-Evidence-Is-Weak-That-Vaccines-Have-Saved-More-Lives-than-They-Have-Cost--&id=520 .