translation.en: So, how we eradicated smallpox was -- max vaccination wouldn't work. You could vaccinate everybody in India, but one year later there'd be 21 million new babies, which was then the population of Canada.
translation.zh: 那我们是怎么根除了天花的呢？要大范围的接种是不可能的 即使今年给全印度的人注射了疫苗，但是下一年马上又有 两千一百万新生婴孩 这相当于加拿大的人口