@WHO: Vaccines go through 3 testing phases before they can be approved: 1⃣ Small scale safety trials 2⃣ Expanded safety trials 3⃣ Large scale efficacy trials The number of volunteers around🌎🌏🌍 increases at each stage to assure #VaccinesWork for many different populations. https://t.co/1jgT1QwYV7

@WHO: Vaccines go through 3 testing phases before they can be approved: 1⃣ Small scale safety trials 2⃣ Expanded safety trials 3⃣ Large scale efficacy trials The number of volunteers around🌎🌏🌍 increases at each stage to assure #VaccinesWork for many different populations. https://t.co/1jgT1QwYV7

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