For example, the cholera vaccine has not been particularly effective. Often the rate of effectiveness is only 50 %, and the period of effectiveness is only three to six months, so it is not widely used.
例如，霍亂疫苗效果不彰，通常有效率只有百分之五十，有效期也只能持續三到六個月，因此並沒有被普遍採用。