Hopkins University Medicine
https://coronavirus.jhu.edu/vaccines/vaccines-faq
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How will we know if a vaccine is safe and effective?
The safety and efficacy of a vaccine is determined through clinical trials. Clinical trials are studies that are typically conducted in three phases to assess the safety and efficacy of vaccines in increasingly larger numbers of volunteers.
Phase 1 clinical trials assess the safety and dosage of a vaccine in a small number of people, typically a dozen to several dozen healthy volunteers. Whether a vaccine stimulates immune responses is often assessed in a phase 1 study but this is better assessed in phase 2 studies, which typically involve hundreds of people including some special groups such as children, people with pre-existing conditions such as heart disease, and older adults. Vaccine safety is also assessed in phase 2 studies, in which adverse events not detected in phase 1 trials may be identified because a larger and more diverse group of people receive the vaccine. However, only in much larger phase 3 clinical trials can it be demonstrated whether a vaccine is actually protective against disease and safety is more fully assessed.
Phase 3 clinical trials often include thousands of volunteers, and for Covid-19 vaccines will involve tens of thousands (30,000 to 45,000 people in some of the ongoing phase 3 trials). In phase 3 trials, participants are randomized to receive either the viral vaccine or a placebo vaccine (sometimes a vaccine against another disease or a harmless substance like saline). Randomization is a process to determine who receives the vaccine and who receives the placebo without any bias, like flipping a coin. To further prevent any bias in interpreting the study data, participants and most of the investigators will not know if an individual received the vaccine or placebo. The participants are then followed to see how many in each group get the disease. If the vaccine is efficacious, many fewer people who received the viral vaccine will get the disease compared to those who received the placebo vaccine. It takes time for cases of disease to accumulate so that we can be confident there is a true difference between the two groups, and this is why these phase 3 trials often take a long time. Assessing safety is also a major goal of phase 3 trials, both short-term safety (e.g. fever, tenderness, muscle aches) and long-term safety (e.g. autoimmune conditions or enhanced disease following infection).
After a vaccine is approved and in more widespread use, it is critically important to continue to monitor for both safety and effectiveness. Some very rare side effects may only be detectable when large numbers of people have been vaccinated. Safety concerns that are discovered at this late stage could lead a licensed vaccine to be withdrawn from use, although this is very rare.
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A me questo scritto e questa accelerazione sull'approvazione del vaccino fanno pensare non poco
e mi fermo qua.
Ma sono un ignorante quindi ….
17 dicembre 2020 - ©Roby2020