“The field of vaccine development, backed up by immunologic theory, has for a long time maintained that as soon as some mishmash of biological matter has acquired the label vaccine by virtue of its ability to induce antibody production, it is immediately assumed to be effective in long-term disease prevention without much further effort to demonstrate this for a fact. For the purposes of demonstrating vaccines’ effectiveness in disease prevention, one random half of the trial participants would be given a placebo instead of the vaccine blindly—that is, without the subjects or the doctor knowing what has been received, and such a trial would have to be continued for many years.
This practice is deemed unethical, because in principle the placebo control group would be left to potentially contract the disease during the course of the trial. Modern biomedical ethics simply cannot let this happen. Therefore, vaccine effectiveness in disease prevention is rarely studied directly. When the disease is not so serious and the vaccine can indeed be studied in this manner, it is done for a short-term only.
But most often, vaccine effectiveness in disease prevention is inferred from its demonstrated efficacy in inducing antibody production and from the interpretation of the disease statistics after the vaccine is introduced into the general population. If the disease incidence goes down after the vaccine is introduced, the vaccine takes the credit. If the disease incidence goes up after introduction of the vaccine, well… Then the conclusion is reached that the vaccine is effective, but simply needs to be given more often.”
— Dr. Tetyana Obukhanych, immunologist
Courtesy: The Outliers