@Marco_Piani No one could be sure of any particular case rate in advance, regardless of strategy. In mid 2020, many places in Europe and a few in the US had near-zero covid. You're not going to spread on purpose just to test vaccines!
@无论采取何种策略，没有人能够提前确定任何特定的病例率。2020年中期，欧洲的许多地方和美国的一些地方出现了接近零的新冠病毒。你不会只是为了测试疫苗而故意传播！