Testing everything under every scenario is impossible. Although as consumers we’d love to see as much testing as possible, funding and timing mean that testing has to be limited. Consequently, scientists have to prioritize the types of tests and the amount of testing a substance or drug undergoes. This prioritization is based on many different criteria such as the substance’s mechanism of action (i.e the way the drug is known to work), data gathered from laboratory and animal testing, as well as plausibility.
Tess is concerned that the measles vaccine is not sufficiently tested in scenarios where there’s no plausible mechanism for harm. The best way to overcome our concerns for insufficient testing is to look at existing data. Often times, we can be surprised by just how much information and testing is out there! Here are some resources: