To be approved, vaccines need to go through multiple rounds of testing to show that they’re safe and effective. A combined phase 1 and phase 2 trial of the Oxford vaccine has demonstrated that it is safe – with only short-term side-effects and no serious unexpected events reported – and that it elicits an immune response. The purpose of a phase 3 trial is to assess whether this vaccine-induced immune response is strong enough to actually protect people from COVID-19. Proving this would pave the way for the vaccine to become publicly available.
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