Generally, Phase III trials are double-blind, meaning that neither the subject nor the administrator knows which subjects are given the actual drug and which are given a placebo. At the end of the trial, that information is revealed and the outcomes are compared. Sometimes the trials are stopped early when an independent monitoring board determines that during the trial, the vaccine has clearly demonstrated it is or is not working, or there are patient safety issues emerging. Phase III trials can get extremely expensive, and pharmaceutical companies don’t like to undertake them unless they
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